Close-up of a male Indian Peafowl's plumageThe male (peacock) Indian Peafowl has iridescent blue-green or green coloured plumage. The so-called "tail" of the peacock, also termed the "train," is not the tail quill feathers but highly elongated upper tail coverts. The train feathers have a series of eyes that are best seen when the tail is fanned. Both species have a crest atop the head.

The female (peahen) Indian Peafowl has a mixture of dull green, brown, and grey in her plumage. She lacks the long upper tail coverts of the male but has a crest. The female can also display her plumage to ward off female competition or danger to her young.

The Green Peafowl is different in appearance to the Indian Peafowl. The male has green and gold plumage and has an erect crest. The wings are black with a sheen of blue.

Unlike the Indian Peafowl, the Green Peahen is very similar to the male, only having shorter upper tail coverts and less iridescence. It is very hard to tell a juvenile male from an adult female.

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. For brown feathers, a mixture of red and blue is required: one colour is created by the periodic structure, and 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 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.