Many of the brilliant colors 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 colors correspond to different length scales of the periodic structures. For brown feathers, a mixture of red
and blue is required—one color is created by the periodic structure, while the other is a created by a Fabry-Perot interference peak from reflections off the outermost and innermost boundaries of the periodic structure.
Such interference-based structural color 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.