Chameleons change color by rearranging tiny nanocrystals in their skin.

A 2015 study by researchers at the University of Geneva, led by Professor Michel Milinkovitch, revolutionized our understanding of chameleon color change. For decades, scientists believed these reptiles relied on the dispersal of pigment-containing organelles called melanosomes. However, the study published in Nature Communications revealed that chameleons possess two thick layers of iridophore cells containing nanocrystals of guanine.The researchers used high-resolution videography and numerical modeling to observe how the lattice of these crystals shifts. When a male chameleon becomes excited, such as when seeing a rival, the lattice of crystals in the top layer of skin expands. This expansion increases the distance between the guanine crystals, shifting the reflected light from shorter wavelengths like green and blue to longer wavelengths like yellow, orange, or red.This process is known as structural coloration, which is the same physical phenomenon that gives butterfly wings and peacock feathers their vibrant hues. Beyond the top layer, chameleons have a deeper layer of iridophores with larger and less organized crystals. These deeper cells reflect a significant proportion of near-infrared sunlight, which likely helps the animal regulate its body temperature in hot environments. This dual-layer system makes the chameleon one of the most sophisticated light-manipulators in the animal kingdom.