Chameleons may make their famously quick costume changes by shifting the positions of light-reflecting cells in their skin, according to a new study.

Most animals who change color do so by expanding, hiding or revealing cells that have particular hues. But according to research published Tuesday in Nature Communications, chameleons can also make rapid changes to structural colors in their skin. Structural colors are created by light refraction instead of pigment — the blue color of the sky is structural, as are the blues of human eyes.

Chameleons do have pigmented cells (in brown, red and yellow) that they manipulate when changing color. But led by Michel Milinkovitch of the University of Geneva, researchers found that they also have two layers of light-reflective cells. Inside these cells are crystals of varying sizes. By relaxing or twitching their skin, they can change the way these little crystals are arranged, thereby changing the way their skin reflects light. 

The researchers also found a deeper layer of these reflective cells. In these cells, the crystals were larger and less ordered. The researchers believe that they're designed to reflect infrared light, protecting chameleons from the heat of intense sun exposure.