Animal colors can come from pigments, such as melanin, or from the interaction of light with regularly-arranged nano-structures in a phenomenon called light interference. The skin of the panther chameleon (Furcifer pardalis) contains an orderly array of tiny crystals made of guanine, also one of the four bases in DNA and RNA. The regular arrangement of the tiny crystals causes a specific wavelength of the incoming white light to be reflected, creating a bright pure color. But the chameleon has the remarkable ability of altering the spacing between the crystals, changing the reflected wavelength, and ultimately its skin color.
This male panther chameleon was photographed in the wild in Madagascar.
Michel C. Milinkovitch PhD, Laboratory of Artificial & Natural Evolution (LANE), Dept of Genetics & Evolution, University of Geneva, Switzerland