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When we look at plants and animals, most of the colors we see--brown eyes, green leaves, yellow sunflowers--are due to the selective absorption of light by pigments. In the leaves and stems of green plants, the chief pigment that absorbs some wavelengths and reflects the wavelengths we perceive as green is chlorophyll. In some animals, color is produced in a different way. The shimmering, intense blue color of the wing of many species of the Morpho butterfly of Central and South America makes colors produced by pigments look flat. When the wing or the viewer moves, the color of the wing changes slightly, causing the shimmering quality we call iridescence. Iridescent colors are found in the wings or feathers of the Oregon swallowtail butterflies, ruby-throated hummingbirds, and many other species of butterflies and birds. Iridescent colors also appear in some beetles, in the scales of fish, and in the skins of snakes. How are these iridescent colors produced? |