How Do Chameleons Change Color?
Chameleons boast some of the brightest colors seen in nature. They can also go from a subdued green to bright red in a matter of minutes. So how do they do it?
Sabrina Stierwalt, PhD
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How Do Chameleons Change Color?
Hi I’m Sabrina Stierwalt, and I’m Ask Science bringing you Quick and Dirty Tips to help you make sense of science.
Chameleons stand out among the lizard species for their uniquely shaped heads, their very long, fast-moving tongues, and their distinct long, thin feet. Due to the subset of chameleons that can change color, they have also long been used in literature, music, and the arts to represent characters that alter themselves according to their surroundings. As Boy George once sang, “Karma chameleon, you come and go.”
For decades, biologists thought chameleons were able to change color using pigments in their skin. However, new research shows that pigments are only a small part of the process. To understand how chameleons are able to transform from bright greens to purples, blues, and oranges and back again, we must first understand how prisms work.
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What is a prism?
A classic prism is a triangular box made of glass or plastic sides that is used to reflect or refract light. Prisms can be used to separate white light into its constituent parts, or in other words, into the separate colors that combine together to make the white light, a process called dispersion. But how do you break apart a beam of light?
Light always travels at the same (finite) speed … in a vacuum, that is. Once light has to travel through another medium, like glass or water, it has to slow down. Light of different wavelengths, or colors, like blue versus red light, will then have slightly different speeds.
When white light enters a glass prism, the light is refracted, and each of its color components is slowed by a different amount and thus bent at a slightly different angle. The other surfaces of the prism can then be used to direct the different colors of light either on paths forward or to be reflected back. 
The behavior of light as it travels through a prism was one of the key discoveries that contributed to our understanding that light can act like a wave and like a particle, a phenomenon known as the wave-particle duality in quantum mechanics.Â
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Chameleons as prisms
So now you may be wondering what all this prism talk has to do with chameleons since they are most definitely not made of glass. Research has recently shown that chameleons are able to produce some of their color changes using a technique similar to that of a prism and not entirely based on pigments in their skin as was previously thought.
The studyopens PDF file conducted by a combination of quantum physicists and evolutionary biologists at the University of Geneva was based on panther chameleons which are typically an olive green in order to blend in with their surroundings. They can change to a stunning red and yellow in a matter of minutes, however, when they are trying to show off, either for a prospective mate or an enemy.
When the biologists looked at the chameleon’s skin under the microscope, they found that while there were pigments capable of producing some of the warmer tones like the dark greens, there were none to explain the bright reds and yellows seen in those reptiles.
Instead they found two layers of cells called iridophores made up of hundreds of thousands of guanine crystals: the first layer showed the crystals in a very ordered, grid-like arrangement while crystals were placed much more at random in the lower layer.
The physicists were able to show in a computer simulation that changing the distance between the crystals would effectively act like a prism to reflect different colors of light. When the crystals were close together, they reflected short wavelengths, or blue, light, while the rest of the colors passed through. When the crystals moved farther apart, the longer wavelength or red light was reflected instead.
These gridded crystals in the chameleons’ skin cells thus appear to act as a “selective mirror” to reflect only certain wavelengths of light, thus changing the chameleon’s color. These different crystal arrangements could, in theory, also work with the chameleon’s pigments to create even more colors, for example, combining a pigmented yellow with a reflected blue to make a bright green.
The biologists took this theory beyond the computer simulation by changing the distance between the crystals in skin cells in the lab. Cells dipped in salt water of varying concentrations swelled to varying degrees thus changing the spacing between the crystals. Their lab results reflected the predictions of the simulations.
Further bolstering the connection between the crystal spacing and the skin color changes is the fact that the female and young panther chameleons, which are not able to change color, do not have the special iridophore cells.
Now what about that second lower layer of cells with bigger, more disorganized crystals? The scientists believe this layer may act to reflect near-infrared light. While reflecting optical light can produce different observed colors, reflecting near-infrared light can act as a cooling mechanism by deflecting the sun’s rays.
Until next time, this is Sabrina Stierwalt with Ask Science’s Quick and Dirty Tips for helping you make sense of science. You can become a fan of Ask Science on Facebook or follow me on Twitter, where I’m @QDTeinstein. If you have a question that you’d like to see on a future episode, send me an email at everydayeinstein@quickanddirtytips.comcreate new email.
