A new study published in Nature Communications shows that the answer is in a lattice of nanocrystals found just under a chameleon’s skin.
Contrary to popular belief, chameleons do not change color to camouflage into the background. Instead, they showcase their colors in mating displays. In this case, researchers took advantage of their social interactions, showing a male chameleon a male competitor and getting him to turn green with jealousy … well, actually more of a yellow-orange. Watch a timelapse of the manly color display here:
The researchers found that the color change was due to the chameleon stretching or relaxing its skin. That movement causes the crystal lattice embedded the skin to change shape, reflecting different wavelengths of light, changing the colors that we see. The researchers also found a layer of skin even deeper inside the chameleon’s skin that seems to reflect near-infrared light. They think that this might be how chameleons manage to keep cool in hot climates.