Ruby red

Hummingbirds are extremely fascinating birds. Perhaps their most famous attribute is their unique flight style with powered wing beast in both the forward and backward direction at remarkable rates of speed, creating the "humming" noise that gives them their English name... In the two shots below my attempts to stop the motion of the wings with shutter speeds below 1/1000th of a second still result in a blur!



But another interesting feature of hummingbirds is the way they derive the colour of their plumage. If you look at the male Ruby-throated Hummingbird below the throat looks black.


But as the head turns the black seems to change to red...

And as is turns more, more red appears

From the right angle the throat ("gorget") is the bright ruby colour that gives this species their name. The reason you can only see the red at certain angles is because the colour is not produced by pigment, but rather by special modification of the barbules of the feathers. Special modifications enlarge certain surfaces to create interference of light waves within each barbule. Some have described the surface of the barbule as like a "tiled floor" or a matrix of keratin and melanin. This interference means that certain wave lengths (colour) are reflected (keratin and melanin have different reflective indices); however, the reflection is also governed by the angle of light.

The result is, of course, splendid!

So I guess the answer to the question when is "black not black?" is "when it is red"!