Splash of Color

A little Jewish girl wearing a red anvil.

Sometimes, in a Deliberately Monochrome work, you'll see an object with a different color. Usually to indicate something important.

Please refrain from telling areas where a movie or show transitions to color. This trope is about colored objects/people within a primarily black and white setting.

Examples of Splash of Color include:

Advertising

Note that when (present day) commercials are shot in black-and-white except for the sponsor's product being in color, the effect is common enough that it's known as "splash of color".
De Beer's diamonds are the only thing that sparkle in a gray world!
One over-the-counter U.S. pain reliever filmed the commercial in black and white, except for the "splash of color" which were the two yellow pills falling out of the bottle into the person's monochrome hand.
- Parodied in Wayne's World: "New. Yellow. Different."
Done to the point of overuse in highlights clips for the BBC's 2008 Olympic Games coverage.
The "Meet the Buttertons" ads for I Can't Believe It's Not Butter feature a typical 1950s family filmed in black and white, except for the bright yellow of the ridiculous amounts of butter they put in their food.
The commercials for Chase bank follow this trope, with the only color being the Chase logo.
- Likewise TD Canada Trust, which are monochromatic except for the green of the bank's logo. The intention is invoke simpler times.

Anime and Manga

Done in Fullmetal Alchemist: Brotherhood, During a monochrome flashback showing Winry's parents death during the Ishval Civil War. All is in black and white except for the blue eyes of the amestrian soldiers and the blue eyes of Winry's parents.

Comics

The Deluxe Edition reprint of Batman: The Killing Joke has the flashbacks sequences in black and white with a different red object, progressively standing out more, to build up to the reveal of the Red Hood becoming The Joker.
Sin City: That Yellow Bastard had Junior (and his blood) constantly colored yellow after the prologue. Other stories, like "Blue Eyes" and "The Babe Wore Red" featured similar use of color. The movie added splashes of color to stories that didn't have them in print.
Wet Moon has no color in the actual stories, but the cover art depicts each individual character with a single thematic color, in their clothing and usually dyed hair.

Films -- Animation

The emotional climax of The Prince of Egypt, where Moses meets with Ramses after his firstborn son is slain, was deliberately rendered in black and white with just a few hints of blue.
At the end of Twice Upon a Time, we see a balloon in the Deliberately Monochrome land of Din turn yellow.

Films -- Live Action

The pre-titles sequence of Casino Royale. The first splash of color in the film is the blood from the gun-barrel (which is moved to the end of that sequence and integrated into the plot—it's the POV from the gun of one of Bond's targets).
In Schindler's List, Spielberg uses red to highlight a single Jewish girl's coat—once as she's being taken to a ghetto, and again as her body is being taken to a mass grave. The candle flames are also in color when the Jews celebrate the Sabbath for the first time since being hauled out of the ghettos and into concentration camps.
The original The Phantom of the Opera is almost all black and white, with the exception of the masked ball scene.
Samurai Fiction, a spoof of traditional samurai epics striving towards art-film stylism, is black and white except for splashes of color used for dramatic effect.
The 2005 remake of The Cabinet of Dr. Caligari has a purple flower that appears near the end of the film.
The 1987 Wim Wenders film Wings of Desire has most scenes filmed in black and white or sepia, except for a few scenes featuring only the female lead, which are supposedly not from the point of view of the angels.
The Spirit is in black and white (though some scenes are so gray they might just be desaturated) except for the Spirit's signature red tie and a handful of other things like yellow police tape and a few closeups with red lipstick.
In Battleship Potemkin, a 1925 silent film, the red flag was colored by hand.
- Even before that film it was done in 1903 in The Great Train Robbery for the gun smoke and some clothing.
Alfred Hitchcock's Spellbound is filmed entirely in black and white, except for a couple of frames of red inserted at the climax when the villain commits suicide.
In Pleasantville, a brother and sister travel back to a 1950s town, which is originally in black and white. Their influence leads people to develop color as they learn to think for themselves.
Person-specific example: In A Muppet Christmas Carol Scrooge dresses entirely in monotone. When he goes out at the end of the film he puts on a red scarf given to him by Beaker, showing his changed personality.
The 1939 The Women is presented in black and white, except for the fashion show sequence, shot in color.
The 1945 The Picture of Dorian Gray is shot in b&w, except for the titular portrait, shown in color.
Likewise for 1948's Portrait of Jennie.
Raging Bull is shot in b&w except for Jake LaMotta's home movies, in color.
In the 1925 silent version of Ben-Hur, all the scenes with Jesus are shot in color (even though he is not shown), as is Ben-Hur's triumph and the final scene.
In The Film of the Book of Rumble Fish, the titular fish are the only things shown in color.
The Film of the Book of The Secret Garden that was made in the forties is entirely in black and white except for the titular garden once the kids restore it.
William Castle's The Tingler is in black and white, but one segment shows red blood in the sink and bathtub in an otherwise b&w shot - impressive effect for a 1959 movie.
- That scene was actually filmed in colour with the bathroom set and actress painted in black, white, and shades of gray.
Nicolas Roeg's Don't Look Now is a color film but shot in very subdued, dark, dingy tones. A red child's coat is made extremely vivid by contrast, and has plot significance.
The Wizard of Oz? Kansas shot in black and white, which switches to omigod!Technicolor when Dorothy arrives in Oz. (The rest of the movie is in color, of course, but the Splash of Color effect when the switch happens is still pretty dramatic. And must have been even more so in 1939.
Abel Gance's 1927 masterpiece Napoleon, shot in black and white, of course, but in the final scenes the screen widens to an amazing 3-screen panorama (25 years before Cinemascope), hand-tinted in blue, white and red to mimic the French tricoleur.

Literature

Every time the word house appears in House of Leaves, it is coloured blue.
Some of Dr. Seuss' earlier books.

Live Action TV

Waking the Dead: "Skin" with some red parts for a tattooing scene, where a guy deliberately infects four neo-Nazis with HIV.
- Also from some episodes with Flash Back scenes during World War Two.
In an episode of Monk, Stottlemeyer's case-solving (which is normally black and white) is showing purple napkins, which were at both places.
In the short-lived series John Doe, the protagonist is colorblind, so the things shown from his point of view are shown in black and white. However, in the pilot, when he sees the news about a missing girl, her face shows color and Doe is convinced the girl is related to him somehow. She wasn't, but every other time the "warning colors" appeared during the series, they were things related to him (like the woman in the green scarf, or the Phoenix statue).
VR.5 played all sorts of games with color during the VR sequences. Typically, unimportant objects were desaturated, while important ones were supersaturated.
Hi Honey, I'm Home! was a reversal of Trapped in TV Land featuring the Neilsons, a family from a 50's sitcom that has been canceled. They are relocated to the Real World, in a typical 90's suburb. When overwhelmed by the complexities of the world in which they now live, they seek comfort by using a device known as a Turnerizer, which causes themselves and their home environment to revert to monochrome. The outside world (as seen through open doors, etc.), as well as anyone from the outside world, are unaffected.
Used extensively in the TV version of Half Moon Investigations for scenes showing how the Crime Of The Week was actually commited (black-and-white otherwise), most notably with spot colour on the pink clothes worn by the Pinks and a yellow jacket that was a Clue. Never two different colours in the same scene, though.
Season 2 of Breaking Bad features several Cold Opens which foreshadow an accident scene, with hazmat-besuited men sifting through debris. The only thing in colour is a pink teddy bear (with an unsettling likeness to |Lotso...)

Music

Italian singer/songwriter Gala's video for Faraway has this.
The video for "The Perfect Drug" by Nine Inch Nails shows everything in blue-tinted monochrome, except for one green drink of absinthe. The ensuing trip switches to a green tint.
The video for "Blame It" by Jamie Foxx shows everything in red-tinted monochrome, except for white camera flashes and blue drink glasses.

Video Games

In The Saboteur, the eponymous protagonist sets about World War II Paris giving the people the will to fight back. Upon restoring a given district's willpower, it will go from black-and-white to dazzling color. Until this happens, however, the only color at all is the bright red on Nazi symbols and the occasional bit of blue on your allies.
In the late-80s Amiga game Wizball, you played a wizard boarding a green bouncing/flying orb with a face in order to bring color back to the various worlds. At first, the worlds were in drab monochrome, but once you directed your cat's own orb to catch enough paint you returned to the lab, after which one of the three colors of that particular world was restored.
In The Legend of Zelda: The Wind Waker, when you first visit Hyrule castle after it's frozen in time, it's completely in black and white. Notable because it's a very sharp contrast to the bright, cel-shaded graphics in the rest of the game, and to Link himself as he is still in color as he runs around.
This was originally planned for the Bonus Level of Tomb Raider 2 Gold, with everything but Lara in black and white and with Lara herself wearing a garish leopard print outfit. Executive Meddling caused this idea to be scrapped (and Lara to be returned to her standard Memetic Outfit.)
Shadow of Destiny revolves around the use of time travel to change your fate—each era you travel to has a different color tone. The modern day is in bright, normal colors, slightly older is a bit off, the turn of the century is black and white, and the 16th century is sepia tone. Oddly enough, your character doesn't change color when he travels, and stands out against the background.
The Eleventh Hour normally plays in color, but has an option to play instead in black and white, with only the puzzles and cutscenes in color. For an added touch, this mode also adds an artificial film grain.
Katamari Forever casts several stages in monochrome, gradually adding color to show which items you're able to collect as your katamari grows bigger.
In Brutal Legend, when the Slies Afire spell is active, the color pallette switches from full-color to black, white, and orange.
MadWorld is always Deliberately Monochrome, except for the bits of yellow in the player's HUD and the onomatopoeia that show up on-screen. And red. Lots and lots of red.
In Dragon Quest VIII, when entering the Dark World your party and Empyrea are in color. Fire and water are also in color.
Mario/Luigi in World 6-3 in Super Mario Bros. The SNES remake, on the other hand, had this level colored normally, which in turn defeats this purpose.

Web Comics

Gunnerkrigg Court's two-page tribute "Metal Gear Theatre" is in sketchy black-and-white, except for a pink sunrise and a red exclamation mark.
- When Annie uses the blinker stone to see into the Ether, any non-magical people and objects are shown in black and white. So, when looking through Ether-vision, the Court becomes grey with some splashes of color, while Gillitie Wood becomes far more colorful.
  - Renard/Reynardine's original body is also in greyscale, since it's waiting for his soul to come back from Annie's plushie. See here.
El Joven Lovecraft is almost completely B&W with very few exceptions like blood.
No Rest for The Wicked is black-and-white except for a few uses of the color red (roses, Little Red Riding Hood's cloak).
Fans had this recently when they needed to point out for plot reasons that two characters (one a parody and therefore inferrable, but the other entirely original) had the same hair color. This came after over ten years of nobody caring.
Ow, My Sanity has the Delta Green symbol and some magic effects, while everything else is black pencil.
The first part of Juathuur is in black and white, save for the occasional color page and Mijuu's blood in chapter 22.
Xkcd does this occasionally.
Dead Winter uses this, all pages are black and white except for the red of Liz's bandana and Monday's shades. Pages that depict the realm of Liz's subconscious are shown in full colour.
In Nip and Tuck, the Show Within a Show Rebel Cry has Green Chicks in otherwise black and white scenes.
- And purple lightning
Archipelago has only magic spells-including telepathic communication-and the cover pages colored.
Terminal Lance is drawn in black-and-white, with the exceptions of reflective belts, which appear a bright vivid yellow.
Wapsi Square is almost exclusively in black and white. However, color is used in Shelly's "boiler room" mental landscape. Unearthly color, but color none-the-less. This is probably to represent the alien, existing on multiple levels of reality nature of the place.
The Mega Crossover fan comic Roommates and also its Spin-Off Girls Next Door are black and white... except for covers and specials. If you see color in the regular pages it's probably there for a reason like in the panel of James' speech.
The flashback sequence of Remus is drawn in greyscale with spots of color for certain eyes, blood, and gunfire.
The comic Namesake uses this. Because the artist does not have time to make the comic fully in color, she limits colors to significant scenes/elements. Ex: Red for the poppies in Oz. To some this is actually part of the appeal of the comic

Web Original

The Asdfmovie series are entirely black and white apart from when blood and rainbows are involved, which is often.
A Beginner's Guide to the End of the Universe has Snuffy the Pooch, imbued with a purple color in the greyscale world.
The Homestar Runner animation "Sickly Sam's Big Outing", presented in "a color!" (pale pink)
- Inverted in "20X6 vs. 1936" where The Homestar Runner is still gray in Stinkoman's otherwise completely colorful world.

Western Animation

The season 1 finale of Avatar: The Last Airbender uses a very dramatic version when Zhao killed the moon. First red light spreads like a bloodstain once the moon spirit/koi is captured and then the entire city loses all color when Zhao kills the moon spirit. Only firebending attacks and Princess Yue's blue eyes are shown in color.
An episode of The Fairly OddParents in which Timmy wishes everything is the same turns everything gray and blobby, leading to Cosmo and Wanda being unable to find Timmy. However, since before the grayification, Timmy's mom tried to make a pink souffle and it collapsed and turned gray, blob-Mom's souffle collapses and turns pink, allowing Timmy to make his signature pink hat and unwish the wish.
- In another episode Wanda disappears and Timmy wishes everything was like a black-and-white noir film, but Cosmo missed a corner of one room.
Animaniacs has a fair share of B&W segments, in all of which the Warners still retain their red noses.
- Including one literal use of this trope: a documentary style interview with an old star about the Warners back in the day has her mention that the Warners would go around "painting the town red, literally". Cut to a shot of them splashing red paint all over a black and white city.