Chameleons are famous for their quick color-changing abilities. It's a common misconception that they do this to camouflage themselves against a background. In fact, chameleons mostly change color to regulate their temperatures or to signal their intentions to other chameleons.
Since chameleons can't generate their own body heat, changing the color of their skin is a way to maintain a favorable body temperature. A cold chameleon may become dark to absorb more heat, whereas a hotter chameleon may turn pale to reflect the sun's heat.
Chameleons will also use bold color changes to communicate. Males become bright to signal their dominance and turn dark in aggressive encounters. Females can let males know if they're willing to mate by changing the color of their skin. Owners of chameleons can learn to read their pet's mood based on the color of its skin.
So how do they pull off these colorful changes? The outermost layer of the chameleon's skin is transparent. Beneath this are several more layers of skin that contain specialized cells called chromatophores. The chromatophores at each level are filled with sacs of different kinds of pigment. The deepest layer contains melanophores, which are filled with brown melanin (the same pigment that gives human skin its many shades). Atop that layer are cells called iridophores, which have a blue pigment that reflects blue and white light. Layered on top of those cells are the xanthophores and erythrophores, which contain yellow and red pigments, respectively.
Normally, the pigments are locked away inside tiny sacs within the cells. But when a chameleon experiences changes in body temperature or mood, its nervous system tells specific chromatophores to expand or contract. This changes the color of the cell. By varying the activity of the different chromatophores in all the layers of the skin, the chameleon can produce a whole variety of colors and patterns.
For instance, an excited chameleon might turn red by fully expanding all his erythrophores, blocking out the other colors beneath them. A calm chameleon, on the other hand, might turn green by contracting his erythrophores and allowing some of the blue-reflected light from his iridophores to mix with his layer of somewhat contracted yellow xanthophores.
With these layers of cells, some chameleons are capable of producing a dazzling array of reds, pinks, yellows, blues, greens, and browns. These bold statements won't help them blend into the background, but they will allow them to get their message across to other chameleons loud and clear.
