Panther chameleon Furcifer pardalis Chameleons can quickly change their appearance in response to temperature, environment, and mood. Scientists recently identified a key factor in their ability to do this: The lizards can “tune” the distances between nanoscale crystals in their skin that reflect light, creating a spectrum of colors. Skin Formed by Layers of Cells Structure Cells Crystals The cells that form its skin play a significant roll in the color changes. This zoom represents 150 microns of a chameleon skin, about twice the diameter of a human hair. How Skin Changes Color Submissive Neutral Excited Intro When the light hits its skin, the cells act depending on the mood of the chameleon. Crystals would be close together in a neutral state and spread out when the chameleon gets excited. This crystals would reflect out to the epidermis the warm light, changing the chameleons color to yellow. Manuel Canales and Daniela Santamarina, ngm staff; Meg Roosevelt. art: Shizuka Aoki sources: Devi Stuart-Fox; Russel Ligon; Kristopher Karsten; Michel C. Milinkovitch, Jeremie Teyssier, Suzanne V. Saenko, Dirk van der Marel (INSET PHOTOS)

Scientists have long thought that chameleons change color when skin cell pigments spread out along veinlike cell extensions.

But Michel Milinkovitch , an evolutionary geneticist and biophysicist, says that theory didn’t wash—there are many green chameleons but no green pigments in their skin cells.

So Milinkovitch and his University of Geneva colleagues began “doing physics and biology together,” he says.

Beneath a layer of pigmentary skin cells, they found another layer of skin cells containing nanoscale crystals arranged in a triangular lattice. (Also see " Amazing Pictures: Baby Chameleon Doesn't Know It Hatched .")

By exposing samples of chameleon skin to pressure and chemicals, the researchers discovered that these crystals can be “tuned” to alter the spacing between them. That in turn affects the color of light that the lattice of crystals reflects.

As the distance between the crystals increases, the reflected colors shift from blue to green to yellow to orange to red—a kaleidoscopic display that’s common among some panther chameleons as they progress from relaxed to agitated or amorous.

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