The coloration of hummingbirds is caused not only by the color | Wildlife

The coloration of hummingbirds is caused not only by the color pigment, but to a greater extent by the interference of light in the beards of feathers. 

This "optical coloration" is inherent in a number of birds, especially tropical ones. The color of their plumage changes when the angle of incidence of light changes, that is, the feathers begin to shimmer when moving.