A Costa's Hummingbird (at least I think it is...) at the Desert Museum in Tucson, Arizona. The feathers that make up a hummingbird's gorget do not directly depend on light absorption and reflection as with most other pigmented substances. Instead, the feathers have a different refractive index than air, so when light is reflected off of them, the beautiful iridescent colors are perceived due to interference coloration. Different colors depend on different refractive indices.

