Carotenoids are a group of pigments responsible for the appearance of the colors red, yellow and orange in a chameleon's skin. Chromatophores that contain yellow carotenoids are called xanthophores, while erythrophores have red carotenoids and are often located close to the outer layers of the skin. When liberating the hormone, intermidin chromatophores contract, liberating the pigments, which causes the skin to change color.
Under the layer of cells that contain carotenoids, there is a layer of refractive cells called iridocytes. Although these cells do not contain pigments, they are involved in the appearance of the color blue because they can refract the blue wavelength of light. The black pigment melanin is found in cells under the layer of iridocytes, but are connected to all skin layers. Melanin is responsible for the darkening of all colors of pigments, also interfering in the darkening of blue hues. Unlike melanin, white pigments are found in guanocytes and are responsible for the lightening of other pigments.
Although most species of chameleons can change the color of their skin to some extent, not all species can do it in the same way and showing the same color range. The majority of chameleon species only show changes in brightness or from the colors green to brown. However, others can feature extreme changes including combinations of greens, blues, black, yellows and oranges.
Changes in light and temperature can cause a chameleon to change the color of its skin. With low temperatures, chameleons tend to turn darker because darker colors can absorb more heat than light colors. The opposite can occur with high temperatures and when the animal is resting under the sun. However, hormonal alterations are the main reason for color change in a chameleon. In the case of the panther chameleon, red and yellow replace its green color when the animal is angry. Males also change their colors to attract females.