Last month, in a post about the green anole, I mentioned that it was able to change color. Anoles and chameleons are not the only color-changing animals. If you’ve ever caught a frog outdoors in cold weather and it seemed to get lighter as it warmed up in your hands, that wasn’t your imagination.
Backyard Biology has a fantastic explanation of frog skin colors and how they can change.
The ever-changeable, Gray Treefrog. How does it do it?
Green is a popular color for frogs, and birds too, but that lovely green color doesn’t come from a green pigment as you might expect, but from the interaction of multiple layers of specialized color and light-reflecting cells in the upper layers of their skin.
Frogs have three layers of chromatophores (color-producing cells) in their skin. The deepest layer are melanophores that produce melanin pigment giving skin a brown to black color. The middle layer are iridiphores which contain no pigment but instead have mirror like plates capable of producing iridescence, or when viewed from a certain angle, reflect blue light. The most superficial layer of chromatophores are xanthophores that contain a yellow pigment. When the middle layer of iridophores interact with the top layer of yellow-pigment containing xanthophores, you get what elementary school students have learned: yellow paint + blue paint…
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Overlooked Nature 