Demonstrating the curious effect of light on feathers are these three photos of the black-billed magpie.
We came across magpies on a Montana back road, shown in the first two photos. Athena captured the iridescent feathers on the wings and tail.
But often, as seen in the third photo taken by a different photographer, the bird shows no blue at all. They look black and white.
Birds get their color in many different ways.
Some birds, like the flamingo, get their color from the food they eat. They eat algae with beta-carotene and as a result, are a pink bird. This kind of pigment coloring is common in many birds.
In other birds, however, the color comes from the structure of the feather and the surrounding light. This is how the blue color is expressed in blue birds.
Light is refracted in the feather by a microscopic structure called a barbule or barb. There are tiny air pockets in the barbules that capture and scatter incoming light.
In both blue- and iridescent-feathered birds, light is the determining factor for the color we see. Bird photographers and birders are acutely aware of this distinction.
Likewise, sometimes we look at a hummingbird and the throat (gorget) looks black. Then the bird turns slightly and you get a riot of color.
It is quite complicated, with varying wavelength refractions, differing species, etc.
Structural coloration is an often-studied concept in nature for application to artificial or manufactured colors. More here.
With some birds, everything in your perspective literally changes when more light is shed on the situation. Another cool thing about birds.
Photo credit: Athena Alexander unless otherwise noted