How do animals create bright blue or green colors without blue or green pigments?

Animals create vibrant blue and green colors without relying on pigments through the production of structural colors, also known as schemochromes. These colors are generated by submicroscopic structures that fractionate incident light into its component wavelengths.1

Mechanisms of Structural Coloration

• Interference: Many iridescent colors, such as those seen on the wings of dragonflies or the feathers of hummingbirds, result from thin-film interference. Light waves reflect off multiple layers of biological structures, reinforcing certain colors while canceling others. These structures are often backed by a dark layer of melanin, which absorbs nonreflected light to intensify the effect.2
• Scattering: Blue colors in many animals are produced by the Tyndall effect. Finely dispersed particles—such as small protein globules or air vesicles—reflect shorter blue light waves while allowing longer wavelengths to pass through to be absorbed by underlying dark pigment.3
• Green Coloration: Most green colors in animals, such as those found in reptiles, amphibians, and birds, are not produced by green pigments. Instead, they result from the combination of scattered blue light passing through an overlying layer of yellow pigment. If the yellow pigment is removed, the underlying structure appears blue.3