Anthocyanins are plant pigments found in leaves, flowers and fruits. Most strikingly, they color autumn leaves red. Over more than a century, biologists have proposed a variety of hypotheses for why colorful autumn foliage should exist, but experiments over the last decade are finally yielding definitve explanations. Anthocyanins protect leaves from damage in at least two ways—by directly shielding chloroplasts from bright light and by scavenging free radicals. It is less clear why plants expend so much energy to produce these new pigments for leaves that are about to die.