英語時差：藍鳥為什不藍？（上）

One of the loveliest sights an ornithologist runs across is the iridescent blue found in some birds’ plumage. Sure, cardinals have red feathers and finches have yellow feathers, but if you ever run across the gleaming, almost metallic-looking blue of an indigo bunting, you won’t forget it. The colors shimmer and shine like oil on water. You might be surprised, then, to learn that the feathers which produce such impressive displays are in themselves largely colorless. Take some cardinal feathers — after the cardinal is done with them — and grind them up into powder. The powder will still be red. That’s because the color is the result of actual pigment in the feather. Take those shiny feathers from a bluebird or indigo bunting and grind them up, however, and their color will disappear. Why?