Birds

From Wikipedia

The male (peacock) has beautiful iridescent blue-green or green coloured plumage. The so-called "tail" of the peacock, also termed as the "train," is in fact not the true tail but the 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 head crest.

The female (peahen) has a mixture of dull green, brown, and gray in her plumage. She lacks the long tail of the male but has a crest.

Females can also display their plumage to ward off danger to her young or other female competition.

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.