Peacocks, nanostructure & iridescence
The spectacular colors of the male peacock plumage are due to an optical interference phenomenon, known as the Bragg reflection, based on periodic nanostructures found in the barbules of their 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, and the other is a created by a Fabry-Perot interference peak from reflections off the outermost and innermost boundaries of the periodic structure.
This interference-based structural color is important in producing the peacock's iridescent hues (which shimmer and change with viewing angle), since interference effects depend upon the angle of light.
Captured with: D700 70-200mm @ f/4.5, 1/160, ISO 800, 200mm. Hand held, with low ambient light deep in a Honduran forest while being propositioned by this aggressive male Peafowl.