There's something special in a blue feather. Unlike feathers of other colors, which are pigmented, bright blue feathers, like these on the vulturine guineafowl, are the result of nanoscale structures in the feather barbs. Microscopic air cavities within the feather barbs are arranged just so to allow coherent light scattering [subscription required], creating a blue hue. Green feathers are typically the result of a combination of blue structural color and yellow pigments.