A male rubythroat's gorget may not always look bright red. Sunlight is the key to seeing the color. The brilliant, iridescent hummingbird colors are caused by the refraction of light by the structures of certain feathers. Like a prism, these structures split light into its component colors; only certain frequencies are refracted back to the viewer's eyes. The apparent color of any particular part of a feather depends upon the distance between the microscopic ridges in its gridlike structure. The resulting colors are much more vivid and iridescent than those of birds with only pigmented feathers. Not all hummer colors are due to feather structure, however; the duller, rusty browns of Allen's and Rufous Hummingbirds are the result of pigmentation. Iridescent hummingbird colors actually result from a combination of refraction and pigmentation, since the diffraction structures themselves are made of melanin, a pigment.
"This hummingbird kept coming to the feeder, but it was in a shadow, so I took this picture of him perching in the nearby Riverbirch tree. The morning sun really helped show off his colors."
Vicki Wisener of Derby, Kansas (Sep. 7, 2013)