Alien Blood



"Well, I see your problem: You're bleeding tang!"

- Nella, The Nostalgia Chick

On the outside, they may be Human Aliens, completely indistinguishable from us Puny Earthlings. Or they can be shapeshifters. Or Rubber Forehead Aliens. Whatever...

What is the best way to quickly establish that a character is not human, sometimes to shock other characters around? Dissection? Squick. They may have Bizarre Alien Biology, but that's usually just an informed characteristic which is rarely appealed to, if ever. Unless it's something very obvious, like having two hearts. Solution? Make them bleed. If their blood is not red, or nonexistent at all, they might as well have the words "NOT HUMAN" written on their forehead.

The trope, of course, is not limited to Human Aliens (Plant Aliens often have green blood, for no apparent reason), but for other types, it doesn't allow for The Reveal in such an effective way.

With Human Aliens, this is a very mild case of You Fail Biology Forever: Since the skin is translucent, a creature with different-colored blood wouldn't have the same skin color as a human...if the skin is white. Darker-skinned aliens, or ones with scales, feathers, hair, or something else hiding their skins avert this problem, albeit probably unintentionally.

Of course, here on Earth, all vertebrates, the largest and most complex members of the animal kingdom, have red blood--the reason? Because all animals breathe oxygen. Red blood cells are red because they contain a protein chemical called hemoglobin, which is bright red in color. This is because hemoglobin contains the elemental metal Iron, which is vital for transporting life sustaining oxygen where it needs to go, and removing waste gases like carbon dioxide. There are other pigments like hemocyanin or chlorocurorin that come in such vibrant shades as pink, orange, blue, and green, but these are much less efficient at transporting oxygen and carbon dioxide than hemoglobin and thus only appear in invertebrates, which have smaller bodies and a better surface-area-to-volume ratio, and thus less need of efficient oxygen transport. Usually hand-waved by having different chemicals in their blood.

In Video Games, Aliens and Monsters often have different colors of blood than red, frequently as an optional mode, to appease the Moral Guardians. Because it's okay to shoot non-human beings if they don't bleed the same way.

Assuming it's not red like human blood, Aliens and Monsters most commonly have blood that's either black or some bright color usually associated with something unhealthy, like orange, green, or yellow (blue and violet are possible, but rare). Robots and Cyborgs, on the other hand, are often shown squirting white fluid when damaged (or black, which is arguably oil). The white blood can be traced back to the android in the movie Alien, who was practically overflowing with the stuff and very squishy compared to most robots in film at the time. In a case of reality imitating fiction perflourocarbon based blood substitutes are white and carry oxygen much more efficiently compared to red blood cells.

Not to be confused with Blue Blood, even if it is, in fact, blue. (Though some blue-blooded aliens can, in fact, be Blue Bloods.)

Anime

 * In Tower of God, Ren's creatures are green-blooded. And orange. And red.
 * The Mulians in RahXephon are Human Aliens with blue blood.
 * The Emilys from Soukou no Strain bleed green.
 * Partially subverted in Tenchi Muyo! when Tenchi was surprised to find that alien princess Aeka had red blood. Villainous Kagato, on the other hand, bled green.
 * In Claymore, the shape shifting, human-eating yoma have purple blood. The titular half-yoma warriors have red blood, normally, unless they Awaken, permanently turning into their Super-Powered Evil Side. From then on, they'll bleed purple.
 * Subverted in Neon Genesis Evangelion, where the robots bleed lots and lots of red, but played straight with the blood of the second angel,.
 * Also played straight with Unit-02, which bleeds purple High-Pressure Blood.
 * While not aliens or monsters, transformed wielders from Witchblade would bleed clear crystalline blood.
 * Judging from the scenes where Nephrite is bleeding and dying, the Dark Kingdom Generals from the first season of Sailor Moon have green blood, even though they have normal human skin tones and the insides of their mouths are pink (as can clearly be seen on any of the numerous occasions when they Evil Laugh).
 * Zoisite, at least, has been shown to have normal red blood (in episode 34 Mamoru injures him with his rose). Nephrite is apparently somewhat of a case of censorship.
 * Kunzite appears to have hot pink blood (in the episode where a Crescent Beam cuts his hands). Perhaps he's a Klingon?
 * In a rather bizarre reversal of this, the aliens Eiru and An from the first arc of the second season have red blood, even though they have green skin and the insides of their mouths are clearly also green.
 * The androids in the Ghost in the Shell series consistently have white blood, a possible reference to the Aliens franchise (See below)
 * Magic-users in Dorohedoro have black particles mixed in with their blood.
 * The Aragami of Blue Seed, being essentially plants, have green blood; this extends to the half-Aragami mutants like Kusanagi, though the latter looks extraordinarily enough not to be mistaken for a normal human. (The color of his blood still helps, considering that he tends to get injured a lot.)
 * In the Hentai anime La Blue Girl, Shikima demons have blue blood; this is also the case of the heroine, Miko Mido (hence the title), since she is half-Shikima.
 * In Dragonball Z, Namekians like Piccolo and Nail bleed purple.
 * Dragonball Z has a few other instances as well. Most villains bled purple or dark red, but occasionally you'd see something weirder. For instance, Zarbon (one of Frieza's henchmen) bled dark blue, which was also reflected in his skin color.
 * On a side note, there was at least one instance of a retconned blood color: Piccolo's blood was red in an early DBZ episode, censored to light green in the dub. It later became purple and was no longer censored.
 * In Interstella 5555, Shep's blood is Yellow.
 * In Blue Drop, the Arume have white blood, as do their halfbreed kids.
 * In Genesis Climber Mospeada (a.k.a Robotech Invids) the aliens learn to get human appearance, however their blood is green, which leads to The Reveal that
 * Most of the Boomers in Bubblegum Crisis tended to bleed bright orange fluid when damaged, which is unusual for robotic enemies.
 * Non-alien example from Naruto: Tobi bleeds white...stuff.
 * The impetus for the war between two groups of people in "Seiketsu no Hagurama", with one side having red blood and the other with blue blood. The main character and Gadgeteer Genius is a blue-blooded prince who discovers to his horror that all his steam-punk looking inventions have been used to eradicate the remaining refugee red bloods by orders of his father and king.

Comic Books

 * Even though he's not an alien, That Yellow Bastard from Sin City had yellow blood, since he's incapable of processing bodily waste, which means his yellow blood is... exactly what it looks like due to Rule of Cool.
 * One character in Hellboy has yellow blood because his body contains the soul of a worm-like demon.
 * Hulk very often bleeds a dark green.
 * Red Hulk has glowing yellow blood.
 * Following Vanya's transformation into the White Violin, she has grey blood.
 * In the (now closed) comics Gea the theme is that extradimentional beings lives on the Earth and are the basis of every myth or religion. As in Men in Black, they try to live under cover, enforced by the Guardians ("Baluardi" in the original), such as the main character. Even when outsiders are outwardly identical to humans (not so common), expect them to be killed in a gore splash of weird blood and alien organs. In one particular case, a team of racist vigilantes kills a group of "outsiders" living in a slum, and are horrified to see that they bleed yellow, smelly liquids. The leader opts for a "foreign disease" and orders the bodies to be burnt.

Fan Fiction
": His blood is the wrong color! The Doctor: Is it?"
 * In the Doctor Who/Firefly crossover The Man With No Name, most oddities of the Doctor's biology are taken from a few of his various serials. One of the few things added by the author was that Time Lord blood is a paler shade of red than a human's.


 * In the Mass Effect/Robotech crossover Protoculture Effect,  is revealed to have green blood when he gets injured.

Film

 * One of the princes in Stardust has literal Blue Blood. Unknown if it's just because he's royalty, or if all inhabitants of the magical world have such blood, since nobody else in the movie is seen bleeding. Word of God states the decision for the color was made to avoid an "R" rating, with the added benefit of being a visual gag for the character.
 * The Xenomorphs in Alien have yellow, highly acidic blood that can burn through steel, while the androids have milky white fluid inside them instead of blood. In the later movies, the blood is green instead, possibly as a result of morphing with human DNA.
 * The Predators from the films of the same name have fluorescent yellow/green blood.
 * Not quite aliens, but one of the first hints that the employees of the Titty Twister in From Dusk till Dawn aren't human is a close-up of a knife which was just used to stab one of them. Instead of blood, it's covered in a translucent goo.
 * In John Carpenter's The Thing, blood samples are taken from all the characters and exposed to heat to test which one is the shapeshifting alien. The alien blood, it turns out, is capable of leaping around the room as an independent organism.
 * The character who proposed and carried out the test did it because he figured that the blood might well do that, as severed pieces had previously been observed operating independently.
 * The monster Gamera has green blood. Not that it's ever likely to be useful as The Reveal, but notable anyhow for the sheer volume you will be seeing in any given movie -- that turtle bleeds like a Garbage Wrestler...
 * His enemy Gyaos' blood was pink.
 * The alien opera singer in The Fifth Element has royal blue blood.
 * Karl Ruprect Kroenen from Hellboy has sand instead of blood. He's not an alien, but a Nazi cyborg zombie who's been through more than Rasputin. It's simply the years of abuse and being in a state of undeath that caused his blood to dry up.
 * Also in the Hellboy movies (and animated movies, but not the comics), Abe Sapien has blue blood.
 * In Hellboy II, the elven royalty has greyish yellow blood.
 * In Star Trek VI the Undiscovered Country, Klingon blood is shown to be Pepto-Bismol pink. Likely done to avoid an R-rating as it ends up being splattered all along the walls of the ship.
 * Also in the movie, there's an inversion where an apparent Klingon's regular red blood leads to the revelation that it's actually a human in a Rubber Forehead Aliens disguise. In the original theatrical edit of the movie, the unmasking scene was cut, making the scene seem like a bizarre oversight.
 * The Moorwen from Outlander has bright green blood.
 * The Strangers from Dark City have black blood.
 * The Strangers from Dark City melt into goo or turn red and dissolve into flakes when they die; the dead human bodies they use as vessels have black blood.
 * The Tall Man in Phantasm gets his hand caught in a door at one point, and the boy cuts off his fingers with a blade. They bleed yellow; the director noted on the commentary that most test audiences were shocked at the unusual color.
 * In Demon Knight The Collector and his minions' blood is green.
 * Buckets of black and green Deadite blood get thrown around in the Evil Dead movies.
 * In Tim Burton's Alice in Wonderland the Jabberwocky's blood is purple.
 * Most of the Graboid blood seen in the Tremors films is an orangish-red color, just different enough from the maroon-red of human blood to avert an R rating.
 * Rahu and Ketu (who are definitely not human)'s blood in The Return of Hanuman is green.
 * In the Disney John Carter Martians have blue blood. Despite all references to their blood in the books indicating that it was red.

Literature

 * The mutants from the future in the Mindwarp kid lit series had metallic silver blood.
 * Many dragons, in all forms of media, have boiling blood, including in the The Malloreon.
 * The main characters in Robert A. Heinlein's The Number of the Beast discover the "ranger" hassling them isn't human when they discover that "he" has blue-green blood.
 * The Orcs in Lord of the Rings and its associated works have black blood.
 * Inverted in Animorphs. Andalite blood is blue-black, but Elfangor and Arbron are squicked out when they find that humans have red blood.
 * And The Devil Will Drag You Under by L. Sprague deCamp had a race of alien demons with blue blood. "Not dark blue, but a nice, pretty sky blue."
 * Discworld elves have green blood too - just like some other famous fictional beings with pointy ears. The explanation is that they have copper based blood, since elves are allergic to iron.
 * In Neil Gaiman's short story A Study in Emerald, an alternate-universe re-imagining of "A Study in Scarlet", the central crime scene is splashed with green blood, since in this universe all those of noble blood are descended from Lovecraftian Elder Gods.
 * In Inheritance Cycle, Lethrblaka blood is bluish-green, like aged copper.
 * The dragons from Anne McCaffrey's Dragonriders of Pern series have green, copper-based blood.
 * Denizens of the House in Keys to the Kingdom have blue blood, and some of them,  have golden blood.
 * The demons in Armageddon: The Salvation Wars have yellow, green, and acid blood.
 * The angels in the sequel have silver or white blood. For both species, blood color was observed to function like blood groups in humans for purposes of transfusions.
 * Unicorns in the Harry Potter universe have mercury-like silver blood, which will heal but Curse you if you drink it.
 * The K'da of Dragonback have black blood, which shows through their scales when they go into battle mode, making them look even more intimidating.
 * Averted in The Forever War. "All God's creatures got hemoglobin"
 * S.L. Viehl's Jorenians have green blood. And a few other odd anatomical traits.
 * In Robert E. Howard's "Rogues in the House", Conan the Barbarian professes to believe that Nabonidus has black blood when offering to cut his throat and see what color it is.
 * It took nineteen books  to find out that Aahz from Myth Adventures has yellow-green blood.
 * Hostess by Isaac Asimov features a race of yellow-coloured, six-legged space cows. Their blood is clear, and Asimov goes into detail as to why that is: they do not require iron in their blood.
 * Elves in Simon R. Green's various urban fantasy novels have golden blood.
 * The Parshendi in The Stormlight Archive have orange blood, chasmfiends have purple blood.
 * bleed blue in J.R. Ward's Black Dagger Brotherhood series.
 * White Court vampires from The Dresden Files have blood that is slightly, yet noticeably paler than that of normal humans.
 * In fact, this trope is so common among the Dresdenverse's many, many kinds of monsters that by the later books, "Bleed for me" has become the standard test for a mortal trying to decide whether to invite a stranger into their home.
 * Humanity in Robert Reed's Great Ship universe have very dark red, almost black blood due to the huge amount of genetic engineering and extra bits of DNA and cells in their bloodstream. The Remoras, twisted by radiation and their own tailored viruses, often have odd blood - one of the characters, Orleans, has very thick black blood.

Live Action TV

 * Vulcans in Star Trek have green copper-based blood, not unlike Earth insects . In the movies, Klingons have pink blood. Ironically, Star Trek VI the Undiscovered Country, which introduced the Klingon Pepto-Bismol Blood, shows a Klingon bleeding red blood in a climactic scene - at least in the theatrical version. Video releases restored a scene cut from the theatrical release explaining this (the "Klingon" is really a human wearing a Rubber Forehead).
 * To a limited extent, Star Trek did Show Their Work in that Leonard Nimoy's make-up did tend towards a more greenish cast than everyone else's. It did take several tries, however, to get this to work the way they wanted when combined with the lighting and the other make-up, which occasionally had hilarious results--especially in early episodes of the show.
 * The shapeshifters of Star Trek Deep Space Nine once caused some paranoia over their infiltration capabilities. As such, Starfleet briefly initiated required blood tests of officers and their family, as any of the shapeshifters' substance removed from their body would instantly revert to their protoplasm. Reassuring? Not quite, as Captain Sisko's father proceeds to point out that if he were a shapeshifter, he'd just kill some poor shlub and use their blood to get around the test. The fact the idea is introduced by someone who later proved to be a changeling infiltrator didn't help.
 * The Andorians have blue blood, which is just icing on the cake since they also have blue skin and antennae. Bolians also have blue blood (and, again, blue skin).
 * While the pigment in Vulcan and Romulan blood may use copper similarly to how human blood uses iron, the pigment would not be all that much like hemoglobin. The usual color of copper-based respiratory pigments in Earth life (which are similar to hemoglobin) is blue.
 * Cardassian blood is black. This also applies to other animal life native to Cardassia Prime, such as the raw fertilized taspar egg Picard ate in "Chain of Command".
 * In the Buffy the Vampire Slayer episode "Earshot", a mouthless demon's fluorescent blood splashes onto Buffy's hand and gives her an "aspect of the demon", which turns out to be hearing people's thoughts.
 * Similarly, in Angel, the title character is "infected" with demonic blood that cures him of his vampirism. It's bright neon green.
 * Power Rangers: A reversal occurs when a villain's human nature is revealed when he does bleed human blood. There was also something of a straight example with Lipsyncher, who "bled" lipstick when her cheek was scarred by Jason's sword.
 * This happened a couple of times in Brimstone, where someone Stone suspected of being one of the 113, was revealed to be human because they bled.
 * The alien human hybrids on The X-Files bled green blood that could produce a deadly gas (to non-aliens) when exposed to the atmosphere, as did the aliens themselves. This got Lampshaded in a heartbreakingly awesome way in "The Unnatural". Ironically, this means that Mulder could see an alien-human hybrid bleeding, and not know there was anything weird going on because he's red/green colorblind!
 * An episode of Stargate SG-1 has the team realize something is amiss when an attempt to draw blood from yields silvery-white fluid instead.
 * While the alien Clark Kent bleeds red blood on the few occasions he's hurt enough to bleed in Smallville, cyborg human Victor Stone (Cyborg of Teen Titans fame) bleeds black mech fluids, keeping in line with the comics. This does not carry over to the Teen Titans cartoon, where it appears to be clear.
 * The alien teenagers of Roswell have both blood and saliva that looks normal to the naked eye but not under a microscope.
 * In the TV series spin-off of V the distinctive reverberation of the Visitor's voices was dropped due to the expense of sound dubbing, and the Visitors were given cliché green blood instead. Some viewers missed the plot point about a human who'd cut his hand actually being a Visitor infiltrator, as they lacked a colour television at the time.
 * Luxans in Farscape have clear blood which turns to black when they get hurt. Black blood is toxic, thus the bleeding has to be stimulated until it turns clear again. Also in Farscape, Nebari have blue blood.
 * Kamen Rider Blade has the Undead, who bleed green. This serves as a Chekhov's Gun as
 * The gun goes off cross-series, as in Kamen Rider Decade,.
 * Doyle, an android in Andromeda "bleeds" superconductor fluid when cut. Due to her in-built Weirdness Censor, she sees it as ordinary blood, thinking herself human.
 * Doctor Who: Time Lords (at least in the Expanded Universe) have blood that's a deep orange. It's sometimes described as basically red, but "orange-ish".
 * In "State of Decay", the Doctor's blood is blue. In every other episode of the series where he bleeds, it's normal red.
 * In the movie it's red, but is different enough from human blood on a cellular level that Grace describes it as "not blood" when she looks at it under a microscope.
 * Babylon 5: The Drazi have white blood. On the other hand, the other major races -- the Minbari, the Centauri, and the Narns -- have red blood.
 * Basco ta Jolokia of Kaizoku Sentai Gokaiger is shown to have light bluish-green blood.

Tabletop Games

 * Warhammer 40000 has a number of different takes on this:
 * Perhaps as an intentional aversion of the 'Human Aliens have coloured blood and pink skin' error, the Tau do not look like humans partly because they have deep blue-purple blood (their equivalent of haemoglobin uses cobalt instead of iron), which has the expected effect on their skin tone. In one of the Ciaphas Cain novels, Amberley Veil notes that it smells horrible.
 * The Orks, who are in fact genetically-engineered carnivorous space-fungi, have green skin but red blood (and mouths). It wasn't always this way and earlier sourcebooks for the game described Ork blood as green, but eventually red gore was decided on. This was explained in White Dwarf magazine with an in-universe biologist's report: while Orks' dense green skin is a chlorophyll- and spore-producing layer, the rest of their body is relatively normal meat, and they have a normal (if supercharged) food-based metabolism to support it. On the same page, the game developers gave the real reason: green injuries on green-skinned aliens were hard to notice, and made the models look like "they've had an accident eating a gooseberry squishy".
 * The Eldar have red blood like humans, but it crystallizes instead of forming scabs.

Video Games

 * Bungie seems to do this quite a bit:
 * In the Halo universe, elites and jackals have purple blood, hunters orange, brutes and prophets red, grunts luminous blue, and drones whitish green. The Flood are a different story: they don't bleed just blood; Infection Forms will liquefy the internal organs of the host, so in reality they're spilling out their entrails in liquid form. Unless the "Grunt Birthday Party" skull is enabled, in which case headshots will cause the grunts to bleed confetti and cheering.
 * In the Marathon series, Pfhor, ticks, lookers and simulacra have yellow blood, hulks blue, S'pht green, and wasps purple.
 * Saga Frontier- Mystics have blue blood, Half-mystic protagonist Asellus has purple.
 * In the Mortal Kombat games, Reptile and (until recently) Sheeva have green blood. Cyborgs have black oil instead of blood, Blaze has molten lava, Noob Saibot has black...wraith juice and.
 * Similar to the Vulcan example above, a major plot point in Star Ocean: First Departure is that Fellpool have copper-based blood - but everyone from that planet has properly pink skin (or tan, in the case of the Highlanders). The only outward difference from humans Terrans is their tails and sometimes fangs.
 * In Mass Effect, a common taunt directed at humans who express conciliatory philosophy toward the varied races of the galaxy is "Do you remember what color your blood is?" Just for fun, stand up to the leader of the isolationist "Earth First (we can exploit the other planets later)" Terra-Firma party.
 * In spite of this, the player doesn't actually see a lot of oddly-colored alien blood in the game, but the Krogan do bleed bright orange and the robotic Geth "bleed" white fluid. The Dr. Saleon sidequest mentions a few other colors in a bit of flavor text at the conclusion of the mission - "pale blue, orange, violet, and more than a few dark red."
 * Thorian creepers don't bleed per se, but they do generate splatters of brownish-green material when they die. There's also a scene where Shepard has the option to Mercy Kill a room of Salarians, revealing orange blood.
 * Oddly enough, Salarians have green blood in the second game.
 * Blood colors in ME also qualify for Shown Their Work credit, as species with alternate colors of blood have skin and/or mucous membrane coloration to match (asari have various tones of blue or purple skin as well as lightly blue-tinged sclerae; krogan, who bleed orange, can exhibit red or yellow eyes; Garrus and several other light-colored turians have a faint purplish cast to their facial features).
 * The krogan have another odd variant on blood, as well. They don't actually have a nervous system made up of nerve cells; rather, they have a second circulatory system consisting of an electrically conducive fluid that runs through their body. As a result, krogan cannot be paralyzed. This physical trait was evolved by just about every species on Tuchanka, the krogan's homeworld.
 * Shown in practice in Mass Effect 2, when gets shot during his recruit mission, and bleeds blue all over the floor, and is later seen with purple scar-tissue over third of his face, mostly covered with cybernetics.
 * In Metal Gear Solid 4 Guns of the Patriots, Super Soldier Raiden has white nanomachine-based blood, the potential symbolism of which is not lost to Vamp.
 * This is a reference to Policenauts, where the "Frozeners" also have white artificial blood, called "first-generation" blood, which is said to be simpler than the "third-generation" blood used on Home (Earth). It's also said to transport oxygen more efficiently than regular blood, making blood loss less of a threat.
 * The aliens (and the cockroaches, which is Truth in Television, see below) in Half-Life bleed light yellow.
 * In the original version of The Legend of Zelda Ocarina of Time (predominately copies of the game with a gold cartridge), Ganondorf coughed up regular ol' red blood after you defeated him. However, Moral Guardians protested that this was too graphic for an E-rated game, and Ganondorf's blood was changed to green for subsequent releases. While this makes sense at first glance (Ganondorf, at least in his Ocarina of Time incarnation, does have rather green skin), it doesn't if you think about it for a while...Ganondorf is the only male Gerudo, and all the female Gerudos (Gerudoes?) you see in the game have peachish-tannish skin...and it wouldn't make a whole lot of sense for the males of a species to have a different color blood than the females, would it?
 * Which is why it was changed again, back to red, for subsequent releases.
 * Interestingly, in Majora's Mask, the enemy Gerudos spray blue blood when you hit them. Hmm.
 * Must be royalty, then.
 * Like in Middle-Earth, in Azeroth orcs (even though they are native to a planet called 'Draenor') have very dark blood, which is why many of the more or less racist humans call them blackbloods.
 * Similarly, the blue skinned draenei have blue blood. That, and their unguligrade appearance has caused a few fans to compare them to the above mentioned Warhammer 40k Tau (although people are even more likely to compare draenei to Protoss).
 * Demon blood seem to be fluorescent green (which is pretty much the trademark colour of fel energy).
 * Sufficiently powerful demons have lava instead of blood.
 * The ant-like enemies found in Jet Force Gemini bleed green blood when you shoot them; and a special "cheat code" makes them bleed rainbow colored blood.
 * The Necris of Unreal Tournament have black blood, though it's not so much of blood as it is a solution of nanomachines they call nanoblack.
 * The Cacodemons and Barons of Hell in Doom appear to leak blue and green fluids when they die, even though their blood spatter when hit while alive uses the same red color as seen for other creatures in the game. Word of God says this is because both do have red blood, but their innards are blue/green. However it has been suggested that they simply didn't have a way to color-shift the red blood splatter sprites and did not want to waste space on differently-colored graphics. Some modern source ports have remedied this by allowing the blood color to be shifted for different enemies.
 * Clowns in Penny Arcade Adventures bleed rainbow colors.
 * In Star Ocean, the Fellpool race has green blood caused by copper used in their blood rather than iron, like Hemocyanin. Somewhat less realistically, it can turn things invisible to most other species.
 * In Blood Omen: Legacy of Kain you play a vampire whose health bar is a blood bar, so NPC blood is Color Coded for Your Convenience: Red blood restores your health, the blue blood of ghosts restores your mana, black blood lowers your health, and green blood poisons you.
 * Like all things Dwarf Fortress, there are different colors of blood based on the creature that bled it.
 * Which, like all things Dwarf Fortress, can be modded to taste. Someone even made a Homestuck (below) troll mod covering the entire hemospectrum.
 * The Maians in Perfect Dark have green blood. The Skedar, meanwhile, have red blood.

Web Comics
"Captain: With pulpy bits? EEEWWWW!"
 * Hall and Eva from Supernormal Step are Type I immortals that bleed black when injured.
 * The alien that attacked Dykowski in Sluggy Freelance has concentrated orange juice for blood. The bad part, according to the crewmember studying the creature, is that it's the homestyle kind.


 * The trolls of Homestuck have a complex caste system based on the color of their blood. Each known troll has a different blood color, spanning the entire color spectrum. The highest castes have literal Royal (Purple) Blood, while the lowest castes have brownish red blood. Trolls higher on the spectrum live longer lives and tend to possess greater physical strength, while rustblood colors tend to have greater psychic powers. Greenbloods (the middle colors) tend to be more emotionally stable. Additionally, Karkat, Kanaya, and Feferi, have rare & special blood-types.
 * Karkat's blood is a mutation -- candy red like human & carapace-person blood. This puts him completely outside (and beneath) the entire hemospectrum and has only been possessed by one other troll in history, his ancestor The Sufferer. As a result, Karkat opts for "blood anonymity" by typing in grey instead of his blood color as all the other trolls do.
 * Kanaya has jade blood, which also lets her enjoy Alternia's blistering sunlight and be awake during the day when the undead normally stir, making her Alternia's Goth equivalent. It also marks her as one of the only trolls to be raised by a virgin mother grub and one responsible for raising its egg.
 * Feferi's blood is literally royal purple, making her heiress to the throne, because it physically grants her protection from the Brown Note of her Eldritch Abomination guardian even at it's highest level.
 * Also, for some reason, troll robots and artificial limbs have blood. Equius uses this to give a rustblood he has a crush on a robot body with blue blood befitting his station. This makes her occasionally prone to violent outbursts, like Equius himself.
 * The Dreamland Chronicles: Nicodemus -- green
 * Terronians in Cordless. Their hair reflects their blood color.

Web Originals

 * Most of the aliens living on Earth in the Global Guardians PBEM Universe bleed red, especially the Tautiq and the Pelkons (who are basically Human Aliens and Rubber Forehead Aliens, respectively). The Delethai are the exception... they bleed orange.
 * Sweet Synn and Black Angel, both of whom are demons in human form, bleed a thick, black ichor that smells vaguely of sewage.
 * Played with to ridiculous amounts in this stickfight where you can find Red, Blue and PINK blood!
 * According to the PPC, Mary Sue characters bleed red or pink glittery blood, or in extreme cases, "only" glitter.
 * Carmilla, a student at the Super-Hero School Whateley Academy in the webfiction Whateley Universe, is mostly-demon, even if she looks like a hot 'urban vampire' goth kid. She bleeds a blackish-purple ichor which is definitely not blood.
 * Same school: Eldritch is a mystical Artificer who bleeds a roughly-blood colored stuff that's too high in metals to be anything a human could have in his/her veins.
 * Squid Kid from Metro City Chronicles has black blood.
 * When the leprechaun in The League of STEAM's webisode "Fool's Gold" is dispatched, he turns into a pile of green goo.

Western Animation

 * An episode of Megas XLR featured a shapeshifting plant alien. Once Coop discovered its true nature, he formed one of the robot's limbs into a chainsaw and got to work. The scene of the chainsaw going into the creature while green goop flies out goes on for over thirty seconds.
 * Kif Kroker bleeds viscous green blood. It's tangy!
 * Agent Bishop (Teenage Mutant Ninja Turtles (2003)) seems to have this as a result of his alien-altered physiology; after he was impaled by a hook in one episode, one could briefly see a thick, silver-colored liquid seeping to his clothes.
 * Invader Zim: A scene near the end of the episode "Lice" seems to show that Zim (and by extension, all Irkens) has green blood, as he's skinned and the tissue underneath is green. Of course, considering that Zim's skin is green, it makes sense.
 * Word of God says that Irkens have see-through pink blood.
 * In the Fish Police episode "The Codfather" when the titular character is murdered (or so we're led to believe) his blood is purple.
 * In the ThunderCats (2011) episode "Ramlak Rising" the Giant Squid/Man-Eating Plant Hybrid Monster the Ramlak is shown to have a strange blue ichor dripping from the severed ends of tentacles that Lion-O slices off when it first surfaces from the Sand Sea and attacks. When Lion-O strikes a mortal blow, its revealed that the monster's blood is, appropriately enough, water.
 * Roger's blood from American Dad is purple.
 * Most of the alien blood in Sym-Bionic Titan is green.
 * Parodied in the The Simpsons, where Moe is trying to convince a group of kids that he's not a troll because he bleeds red. Then he nicks his finger, and a frustrated Moe sees green blood spurting from the wound.

Real Life

 * While certainly not aliens, most insects bleed light yellow (as mentioned above), some green, molluscs and crustaceans bleed blue.
 * The most famous of these is the humble Horseshoe Crab, with blue copper-based blood. Scientists routinely extract blood from the crabs for all kinds of medical procedures & tests, then release the animals after they've regenerated their blood.
 * Inverted with deep-sea tube worms, which have red blood like ours despite being from a taxonomic line in which iron-based blood pigment isn't expected.
 * The trope of artificial humans having white blood possibly comes from the early research into oxygen-carrying temporary blood replacements for emergency surgery. Some of these work using very different chemical processes to naturally occurring blood (of any colour) and look a lot like milk.
 * Sulphur can turn a person's blood green.
 * And carbon monoxide poisoning turns it an even brighter, unnatural-looking shade of red.
 * Underwater, red blood appears green below a certain depth.
 * The Prasinohaema genus of skinks, in contrast to every other healthy vertebrate, have green blood (as well as green muscles, bone, and everything else). This is caused by levels of biliverdin (bile pigment) in the blood that are so high they would kill any other vertebrate.
 * There is a species of pen shell called Pinna Squamosa. What makes it unique is that it is the only mollusc to use manganese to store oxygen, in a protein called pinnaglobin. As a result, it has brown blood.
 * Scientists are getting in on the fun too, it seems. They have created a oxygen-binding molecule called coboglobin, which is based on cobalt. Like human blood, it changes colors based on if it's oxygenated or not. If it is, then it's clear; if not, it turns amber yellow.
 * A convention of anatomical illustration is that deoxygenated blood vessels are depicted in blue on drawings and models. This sometimes leads people to the false conclusion that deoxygenated blood is blue; in fact, it's a reference to how the outsides of systemic veins, which carry this type of blood, look blue when seen through the paler shades of human skin.
 * While their actual blood doesn't look different, the bone marrow of a patient with advanced leukemia looks lighter in color than that of a healthy person, due to being overloaded with immature, non-functional white blood cells.
 * There is a disorder called hemocyanosis in humans. A portion of their hemoglobin slowly gets converted into an inert, de-oxygentated form because the enzyme that should revert it to the active form cannot operate on it. If they have only one of the six genes that code for hemoglobin proteins affected, it doesn't produce symptoms beyond a bluish discoloration of the blood and skin (doctors who don't know or recall this disorder exists may start looking for heart or lung problems that don't exist, and some of the tests can be dangerous). A person who gets more than one gene affected can start to get into trouble. This is the origin of the term 'blue-bloods' for certain old monied families in Boston, where the first form of the disorder was identified.
 * Due to having little to no hemoglobin, Antarctic icefish have translucent white blood.