This video says about itself:
3 July 2016
The feathers on this hummingbird’s throat are surprising. One minute they’re bright red, the next, black. This is known as iridescence, a common, showy feature of many birds’ plumages, from hummingbirds to starlings to jays to ducks.
Iridescence doesn’t exist as a pigment—it is a structural color created by light striking the feathers. In each iridescent feather, keratin, melanin, and air are arranged in such a way that the appearance of the feather changes at different viewing angles.
Hummingbird migration: here.