How do chameleons change skin color?
The study involved males of the Madagascar panther chameleon (Furcifer pardalis), who can change color from blue-green to bright red and vice versa in a few minutes. It is known that a color change is associated with the work of special skin cells - chromatophores that redistribute pigments of four colors. Pigments reflect visible light in a narrow spectral range, but now scientists have found that for chameleons, iridophores are much more important - cells that do not absorb light, but reflect it.
The skin of the chameleons was carefully examined using an electron microscope and two layers of iridophore were found in it, and the upper layer contains guanine nanocrystals organized in the form of a clearly structured lattice. The lattice pitch (the distance between the crystals) plays a key role in the color change - as it increases, the maximum wavelength of the reflected light shifts to the long-wave (red) region, and when it decreases, to the short-wave (blue) region. By changing the lattice pitch by stretching or reducing the layer of iridophores, chameleons adjust the color to the surrounding environment.
Chameleons also have a second, more deeply located layer of iridophores, with a large spacing of the lattice of nanocrystals. The maximum reflection of this layer is in the infrared region of the spectrum. Presumably, this layer in chameleons is an important mechanism of protection against overheating in hot conditions. Scientists suggest that a similar mechanism can be used to create new artificial materials that can change color.