Most people think frogs are green, right? And it’s true, most frogs are a greenish, brownish, yellowish color, the better to hide from predators among grass and other vegetation.

But frogs can be many different colors, even bright crayon colors like sky blue.

This three-centimeter-long blue tree frog in a tree in Chofu, western Tokyo. Courtesy of Toba Aquarium, Japan.

Why would a frog species evolve such a bright vivid color that would make it stand out? In most cases the frog, such as the colorful dart frogs, are giving a strong warning to predators: Don’t eat me! I’m poisonous! Either through instinct or through learning the hard way, predators will avoid them. These brightly colored frogs contain poisons that can kill or paralyze an animal that comes into contact with it.

The frog’s skin is not actually blue. The color comes from layers of chromotophores, or pigment-containing and light-reflecting cells between the dermis and epidermis (inner and outer skin layers). A blend of the three types of chromatophores creates the color, or in some cases, even transparency:

melanophores: contain pigments that appear black or brown from melanin

xanthophores: contain yellow colored pigments

iridophores: contain reflective or iridescent pigments

So although most of the time, frogs are green, sometimes Frogs Are Blue!