Many chameleons (especially of genus Furcifer) can change color extremely rapidly not only for camouflage, but also for communication, courtship, and contests. A recent study finds that complex and quick color changes are attributed to two layers of skin that contain crystals that reflect light. The double layer of skin also may provide thermal protection in cooler weather.
[Photo by Meredith Lutz; caption by Maggie Creamer]
Teyssier, J., Saenko, S. V., Van Der Marel, D., & Milinkovitch, M. C. (2015). Photonic crystals cause active colour change in chameleons. Nature communications, 6, 6368.