Chameleon turquoise, and purple. Chameleon skin has a superficial layer which contains pigments, and under the layer are cells with guanine crystals. Chameleons change colour by changing the space between the guanine crystals, which changes the wavelength of light reflected off the crystals which changes the colour of the skin. Colour change in chameleons has functions in camouflage, but most commonly in social signaling and in reactions to temperature and other conditions. The relative importance of these functions varies with the circumstances, as well as the species. Colour change signals a chameleon's physiological condition and intentions to other chameleons. Chameleons tend
Snow camouflage snow camouflage patterns. Charles Darwin mentioned the white winter coloration of the ptarmigan in his 1859 "Origin of Species": The white protective coloration of arctic animals was noted by an early student of camouflage, the naturalist Alfred Russel Wallace, in his 1889 book "Darwinism"; he listed the polar bear, the American polar hare, the snowy owl and the gyr falcon as remaining white all year, while the arctic fox, arctic hare, ermine and ptarmigan change their colour, and observed "the obvious explanation", that it was for concealment, at a time when Darwinism was at a low ebb. Later zoologists such