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— Illustration by Matt Patterson in “The Snake and the Salamander”

The green frog actually has no green pigment in its skin, explains Alvin Breisch in his new book. The green color is the result of a mix of the specialized cells in the skin called chromatophores — the uppermost layer, the xanthophores, contains yellow pigment. Under that layer are the iridophores, which reflect light, giving the skin a blue appearance. When the two are combined, the frog appears to be green. When the yellow is missing, the frog’s skin appears blue. “The Green Frog’s distinctive call, like a plucked out-of-tune banjo, is a welcome sign of summer,” writes Breisch.