Many of the brilliant colours of the peacock plumage are due to an optical interference phenomenon (Bragg reflection) based on (nearly) periodic nanostructures found in the barbules (fiber-like components) of the feathers. Different colours correspond to different length scales of the periodic structures.

Such interference-based structural colour is especially important in producing the peacock's iridescent hues (which shimmer and change with viewing angle), since interference effects depend upon the angle of light, unlike chemical pigments.