Although it's commonly believed that chameleons change color simply to blend in with their surroundings, it can be due to a range of environmental and emotional factors. It's unclear whether these lizards actively tell their body to change color or if it's an automatic response, but they do need to instruct it which color to change to.
Meet the Chameleons
Around 90 species of chameleons exist worldwide, with adults ranging in size from 4 to 24 inches. These lizards all belong to the taxonomic family Chamaeleontidae. In the wild, these creatures can be found in Sri Lanka, Spain, Africa, Madagascar and India. They're arboreal lizards, which means they spend their lives in trees, where there's plenty for them to eat and it's easier to hide from potential predators. They can rotate their distinctive eyes independently of one another.
Why Change Color?
While many people believe chameleons change color to camouflage themselves with their surroundings, they most commonly use it as a way of signaling others of their species. When males are challenged by others of their sex, they'll start flashing their brightest colors at each other to try to assert their dominance. When these creatures want to breed, they'll turn a mixture of all the colors they can muster up to show others of their species that they're in the mood. They also may change color in response to environmental factors, such as temperature and lighting.
Anatomy of a Color Changer
The outer layer of chameleon skin is transparent, whereas the layers beneath contain different pigment cells -- known as chromatophores -- which allow them to change colors. The first layer of pigment cells are xanthophores, which contain a yellow color. The second layer of specialist cells are red-colored erythrophores. The next layer contains iridiphores, which have a blue color. The fourth and final layer of pigment cells are melanophores, which contain a brown color.
While chameleons have all these layers of color in their skin, the pigments are kept in miniscule vesicles that stop the colors from appearing. In unremarkable conditions, their skin is a green-brown color. When they want to change color, they must first assess the situation and decide what hue they want to adopt. Then they release hormones from their brains to instruct their body to make the change. When the signal from the hormones have been received, the vesicles can release the appropriate pigments, which then coat the chromatophores, allowing the colors to appear.