Butterflies are well known for the beautiful colors and patterns that decorate their wings. These can benefit the butterfly in a number of ways, including attracting mates, providing camouflage, or warning predators that they are distasteful. Many of the colors are created by pigments within the scales of the wing, but other colors, especially blues and greens, are instead produced by a remarkable phenomenon known as structural coloration.
Pigments are molecules that absorb specific colors, and the colors that remain are reflected and create our perception of the color of the wing, but in the case of structural color, nanostructures, smaller than the wavelength of light, cause the amplification of certain colors, and the diminution of others, to create dazzling hues. While the physical basis of structural color is well understood, we know very little about how animals and plants create the nanostructures required to create the optical effect. Nipam Patel describes a number of butterfly species that use structural coloration, and recent developmental, genetic, and cellular insights into how scale cells generate the necessary materials and geometry to create these colors.