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Swiss researchers have discovered how chameleons accomplish their vivid colour changes: they rearrange the crystals inside specialised skin cells.
It was previously suggested that the reptiles' famous ability came from gathering or dispersing coloured pigments inside different cells.
But the new results put it down to a "selective mirror" made of crystals.
They also reveal a second layer of the cells that reflect near-infrared light and might help the animals keep cool.
Reptiles make colours in two ways: they have cells full of pigment for warm or dark colours, but brighter blues and whites come from light bouncing off physical elements like these crystals: so-called "structural colours".
"Chameleons invented something completely new in evolution," Prof Milinkovitch said.
"They split the iridophores into two layers, one that is specialised for colour change... and one to reduce the amount of energy absorbed by the animal.
"That's an amazing toolkit that allows them to choose between being hidden or displaying very spectacular colours for communication - and on top of that they have this ability to control their temperature because of the deep iridophores."