Why and how do chameleons change color, not other animals can?

When most people think of colour change, they think of octopuses or chameleons - but the ability to rapidly change colour is surprisingly widespread. Many species of crustaceans, insects, cephalopods (squid, cuttlefish, octopuses and their relatives), frogs, lizards and fish can change colour. read more

Unlike other animals that change color, such as the squid and octopus, chameleons do not modify their hues by accumulating or dispersing pigments within their skin cells, the researchers found. Instead, the lizards rely on structural changes that affect how light reflects off their skin, the researchers said. read more

actually you’re wrong! some octopus species can change colour, as can cuttlefish. They change colour as a defense mechanism to hide from predators read more

So a calm chameleon is a pale greeny colour. When it gets angry, it might go bright yellow, and when it wants to mate, it basically turns on every possible colour it can which shows that it's in the mood. This is not unique to chameleons. Other animals also have these chromatophores. Cuttlefish are another very elegant example of how this works. read more