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 times longer to detect than older NATO camouflage which worked at only one scale, while recognition, which begins after detection, took 20 percent longer than with older camouflage. Fractal-like patterns work because the human visual system efficiently discriminates images which have different fractal dimension or other second-order statistics like Fourier spatial amplitude spectra; objects simply appear to pop out from the background. Timothy O'Neill helped the Marine Corps to develop first a digital pattern for vehicles, then fabric for uniforms, which had two colour schemes, one designed for woodland, one for desert. Multi-scale camouflage Multi-scale camouflage is a type of