Chameleons change colour by tuning a lattice of nanocrystals in their skin

Scientists long assumed chameleons shifted colour purely by moving pigment inside cells. A 2015 study found a second skin layer packed with a lattice of guanine nanocrystals; relaxing or tensing the skin stretches the spacing between crystals, changing which wavelengths of light bounce back. That physical trick lets a panther chameleon flip from camouflage green to a flamboyant display in seconds.

— Jeremie Teyssier, Suzanne V. Saenko, Dirk van der Marel, Michel C. Milinkovitch, Photonic crystals cause active colour change in chameleons — Nature Communications, 2015