Hollywood Chameleons

In Real Life, Chameleons have only a limited colour changing ability which is primarily dictated by the lizard's mood. It is only rarely used for camoflage, despite the common perception, and even then only in some species. In reality, the colours they change into (shades of green, brown, and grey, with bolder psychedelic patterns usually reserved only for courtship/frightening rivals and predators/etc.), just happen to be the same as their surroundings most of the time.

Fiction chameleons, of course, can seamlessly will their skin into an exact reproduction of whatever they're standing in front of. A few more fantastical chameleons can straight-up become invisible or even transform!

As a side note, the most well-known animal that actually does this is the octopus (along with cuttlefish), a trait rarely attributed to it in fiction. Meanwhile, the camouflage thing isn't the only behavior which has been falsely attributed to chameleons: in the Middle Ages and Renaissance, it was popularly believed that these lizards lived by eating nothing except air. The title character of Shakespeare's Hamlet references this, claiming to to the same thing himself (during his period of feigning madness).

Subtrope of Somewhere a Herpetologist Is Crying. Compare Invisibility Cloak.

Anime

 * In Naruto, a giant one of these a person can hide in is one of Animal Pain's many summons.
 * In Digimon, Chamelemon can appear to disappear even if they're not standing up against anything.
 * In Yaiba there's Chamaleon Bonaparte, a french-speaking chamaleon who could not only turn invisible but even transform into another character

Comic Books

 * The title character from British comic strip Kid Chameleon was raised by lizards and wore a skin-tight suit of chameleon scales (and not much else). By concentrating, he was able to make the scales change colour, turning him almost invisible - except for his prominent mop of blond hair, which somehow the bad guys never noticed.
 * Anole from The New Mutants has this ability.

Film

 * Subverted in Doctor Dolittle 2, with Papito the chameleon, who thinks he has the ability to blend completely into the background, but never can. At the end, Charisse paints a room completely green as a surprise for Papito, and it looks like he finally got his dream.
 * Played With in Tangled with Pascal, who mostly changes with his mood, it's just that half the time he happens to be in front of something of the same colour.
 * Except the first scene with him, when he tries to blend in with a colourful pattern by appearing as this pattern. It doesn't work.
 * Randall, a monster based off a chameleon, from Monsters, Inc. is an extreme example. He's completely invisible not only when standing against a background, but even when standing in the open and in physical contact with someone else.
 * Averted with the main character in Rango, whose colour-changing abilities are more in keeping with a real chameleon's ("It's an art, not a science!"), which doesn't do him any good when trying to hide in the desert. He does a moderately better job at imitating a packet of licorice while hiding in a sweets machine, although he's found out anyway.

Literature

 * In Michael Crichton's The Lost World, the Carnotaurus had extremely complex colour-changing abilities, being able to mimic the appearance of its surroundings, including a chain-link fence.
 * As an aside, Chrichton was aware of how -to put it gently- unlikely this would be. He explained that he decided to essentially turn Carnotaurus into the Predator just to see how Steven Speilberg would handle the effects in The Film of the Book. (And then they aren't included in the film, which goes in a completely different direction. Cue sad trombone.)
 * Similarly, it appears as though Ceratosaurs have this ability in Age of Reptiles. It's a tad bit jarring.
 * The Eric Carle story The Mixed-Up Chameleon has a chameleon that behaves as a normal chameleon does, until it visits a zoo one day and suddenly starts wishing to be more like the animals it sees, which ends up turning it into a Mix and Match Critter.
 * A storybook by Leo Lionni was also about a chameleon that can change colour this way. He angsts over it because he feels this means he doesn't have an identity of his own. Until he meets a lady chameleon, who explains that "we can be all different colours together". D'aww.
 * The protagonist of the picture book Chameleon Was a Spy by Diane Redfield Massie is capable of matching backgrounds and reproducing complicated patterns; it's a plot point that he's even capable of manipulating his pigment to form writing.
 * Exaggerated in A Spell For Chameleon--the things referred to as chameleons in-setting definitely aren't, and are capable of disguising themselves as other species.
 * Justified (?) in Stationery Voyagers when the devil himself assumes the form of a chameleon. He has a different colour for every limb, just to flaunt that he can look like whatever he wants to.
 * In The Wishsong we get one of these... As a giant tiger. (The Cheshire Cat reference is obvious.)
 * Actually subverted in a book where a kid buys a chameleon because he's seen how they can apparently change to any colour. Turns out they can only turn brown or some other colour, and the kid is understandably disappointed.
 * This is likely based on a weird Real Life case of Call a Smeerp a Rabbit. The Carolina Anole, a small tree-dwelling Iguanid, used to be sold in pet stores under the name "Chameleon". The only reason for this was because the Anole can change from green to brown depending largely on health or temperature; they look nothing like a real chameleon and are nowhere near closely related. Nowadays, their usually simply sold under their real name... which can lead to a bit of confusion when they are called Chameleons in older media.
 * In Dark Life, this is  Interestingly, Dark Gifts are based on the abilities of sea creatures, so this fits under the octopus example.

Tabletop RPG

 * The Mokole from Werewolf: The Apocalypse have this as a possible character trait. This error feels rather blatant considering all the research that went into reptiles for the book.

Video Games

 * One boss in Kirby Super Star is this. He can turn practically invisible.
 * Kecleon from Pokémon Ruby and Sapphire, aside from its belly stripe, which never changes.
 * The Sonic the Hedgehog character Espio's ability to blend into any colour is represented by him becoming almost invisible. In Sonic Heroes, he can use this ability to literally walk through laser detection systems without being spotted by them.
 * The chameleon in Impossible Creatures has the Camouflage ability, which makes part-chameleon creatures invisible. It shares this ability with the rattlesnake and walking stick, which make it even more ridiculous considering they only blend in with specific surroundings.
 * The final boss in the Tarzan level of Kingdom Hearts was one of these.
 * The Carnotaurus in The Lost World arcade game had chameleon abilities like its novel counterpart, but the way it looked in the game was more along the lines of a cloaking device.
 * Sting Chameleon in the first Mega Man X game could blend into the background and avoid X's weapons, though it's more of a cloaking field than color change. His weapon, when charged, causes X to flash in a rainbow of colors and be invisible and invincible while it lasts.
 * Francis from Super Paper Mario.
 * The blabbermouth boss Cameo Leon in Viewtiful Joe 2. Justified in that he's a robot.

Web Comics

 * The Perry Bible Fellowship: "Love Lizard"

Western Animation

 * The Disney film The Wild
 * One Looney Tunes short had a chameleon who shows off his colour changing abilities, but breaks down when he finds a plaid backdrop.
 * In a Shout-Out to this, the character Camo-Man (not Camel Man) in Duck Dodgers is only visible in front of plaid.
 * Also, The Crusading Chameleon in The Tick (animation) actually loses consciousness when he encounters this pattern.
 * The chameleons in The Penguins of Madagascar use their colours as a means of communication
 * In the animated film Katy Caterpillar, the titular character meets up with a group of chameleons who can change to "any colour of the rainbow" and even two colours at once, and look down on anyone who can't change colour.
 * The Simpsons, "Alone Again, Natura-Diddly": A chameleon living on a racetrack changes colours to exactly match an STP can. It then gets eaten by a snake living in the can, regardless of the perfect camouflage.
 * An episode of the 90's remake of Secret Squirrel had a chameleon as its villain--an art thief who could blend himself in perfectly with fine art. Like the Looney Tunes one broke down in front of plaid, this one completely broke down when he stood in front of modern, abstract pieces.
 * My Gym Partner's a Monkey, after an advertising executive abused Ms. Chameleon's colour-changing abilities for a TV commercial, she was unable to stop changing colours.
 * In the Phineas and Ferb episode "The Lizard Whisperer", the boys' pet chameleon Steve can straight-up disappear. Of course, that inspires Ferb to give his longest speech ever, so we're not complaining.
 * In Rocko's Modern Life, the Chameleon Brothers don't actually change colour...but they do change jobs a lot, based on what's trendy.
 * Taken to a new level with The Chameleon. His camouflage consist in actually transforming in what he wants.
 * Can be seen as an aversion too, since he can only do it with his special suit. Without it, he is just a normal chameleon.

Real Life

 * Cephalopods in Real Life are more like Hollywood Chameleons than real life chameleons
 * The cuttlefish, in particular, can blend in with a checkerboard, or put on a hypnotic display of undulating lights.
 * A mimic octopus can mimic a Banded Sea Krait, a venomous elapid snake, by changing colour to black and white rings. It even mimics the shape and swimming style of the Banded Sea Krait.