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
Underwater camouflage bottom-living fish such as the flounder can hide themselves effectively against a variety of backgrounds. Many cephalopods including octopus, cuttlefish, and squid similarly use colour change, in their case both for camouflage and signalling. For example, the big blue octopus, "Octopus cyanea", hunts during the day, and can match itself to the colours and textures of its surroundings, both to avoid predators and to enable it to approach prey. It can perfectly resemble a rock or a coral it is hiding beside. When necessary, in order to scare away a potential predator, it can display markings which resemble eyes. Like