As with many birds, vibrant iridescent plumage colours are not primarily pigments, but structural colouration. Optical interference Bragg reflections based on regular, periodic nanostructures of the barbules (fiber-like components) of the feathers produce the peacock's colours. Slight changes to the spacing of these barbules result in different colours.
Brown feathers are a mixture of red and blue: one colour is created by the periodic structure and the other is created by a Fabry–Pérot interference peak from reflections from the outer and inner boundaries. Such structural coloration causes the iridescence of the peacock's hues. Interference effects depend on light angle rather than actual pigments.