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Iridescence

A brilliant topic

A peacock’s tail is actually brown. But it possesses structural surface properties that create a bright rainbow of hues. The colorful display is due to iridescence.
    The simplest example of iridescence is the colorful shine of a drop of oil floating on water. When the oil film is thin enough, light gets bent as it hits the oil-water interface in a process called refraction. That light may be only one wavelength, one color, as determined by the thickness of the oil. The thinner the oil, the shorter wavelength of light that bounces back. The thicker spots are reddish and the thinner bluer.
    Animals of all sorts have created structural coloration not from pigments. In some, like a snake called the rainbow boa, it is from a thin film that changes thickness and color as the snake stretches and compresses while moving. Other colors are created by a static bio-coating or structures that create refraction of a particular wavelength, as with the peacock or the throat patch of a ruby-throated hummingbird.
    The angle of the light hitting the throat patch sometimes hits that sweet spot where the refraction amplifies the bounced light. In the photos presented here —taken within two minutes — the light was too bright for my camera’s sensor. 
    Iridescence is used for coloration by many plants and animals. It is, however, uncommon in mammals. 
    Look around and decide if the color you see is due to pigment or to light-bending iridescence.