The variety of colors that chameleons can display is produced through a combination of pigments and structural colors. Chameleon skin contains different types of chromatophore (color-bearing) cells organized in layers within the skin. The upper layer of skin contains cells with yellow and red pigments, while lower layers contain cells with dark melanin pigment, which appears black or brown. Just below the layer of yellow and red chromatophores is a layer of cells called iridophores (iridescent chromatophores) that produce structural color. Rather than containing pigment, iridophores contain an organized array of transparent, nano-sized crystals that reflect specific wavelengths of light. The reflected light is perceived as color.
The latest research on color-changing in chameleons reveals that they primarily change color by actively adjusting the spacing between these nanocrystals, which causes different wavelengths of light to be reflected. The crystal structures and pigments in chameleon skin both contribute to the overall color of the skin. For example, when blue light reflects off the crystal layer and travels through the yellow pigment above, the result humans see is the color green.
Researchers are still investigating the function of changing skin color in chameleons, but more recent research suggests that chameleons change color to communicate with one another during social interactions.
Check out this video by KQED Deep Look to learn more about how chameleons change color, and about how researchers are building synthetic chameleon skin that mimics these lizards’ color-changing mechanism.
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Historic and contemporary theories on chameleon color change
The discovery of the mechanism of colour-changes in the chameleonAnnals of ScienceJune 8, 2006
Principles of Animal Communication, Second EditionAugust 3, 2011
“Many vertebrates can rapidly change colour for camouflage, communication and thermoregulation2, 4, 5, 6, 7, but these so-called physiological colour changes are generally mediated by modifications of skin brightness (that is, diffuse and/or specular reflectivity) through dispersion/aggregation of pigment-containing organelles, especially melanosomes, within dermal chromatophores6, 7. On the other hand, rapid active tuning of skin hue has been described in only a handful of species and generally involves structural, rather than pigmentary, components, that is, multilayer nano-reflectors with alternating high and low refractive indices that generate interference of light waves…
…chameleons have evolved two superimposed populations of iridophores with different morphologies and functions: the upper multilayer is responsible for rapid structural colour change through active tuning of guanine nanocrystal spacing in a triangular lattice, whereas the deeper population of cells broadly reflects light, especially in the near-infrared range. This combination of two functionally different layers of iridophores constitutes an evolutionary novelty that allows some species of chameleons to combine efficient camouflage and dramatic display, while potentially moderating the thermal consequences of intense solar radiations.” (Teyssier et al. 2015:2)