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
Multi-scale camouflage and overall disruptive effect. A failure to consider all elements of pattern design tends to result in poor results. The US Army's Universal Camouflage Pattern (UCP), for example, adopted after limited testing in 2003–4, performed poorly because of low pattern contrast ("isoluminance"—beyond very close range, the design looks like a field of solid light grey, failing to disrupt an object's outlines) and arbitrary colour selection, neither of which could be saved by quantizing (digitizing) the pattern geometry. The design was replaced from 2015 with Operational Camouflage Pattern, a non-pixellated pattern. The idea of patterned camouflage extends back to the interwar