Ecologists have long wondered how two coral reefs—sitting right next to each other in the ocean—can be drastically different shades of color. The answer, according to a new study, has to do with some intriguing genetics. By sequencing three colonies of Acropora millepora, a branching stony coral obtained from the waters of Fiji, scientists have discovered that instead of having one gene that controls pigment production, these corals harbor multiple copies of the same gene. The more genes the corals activate, the greater their strength of color, researchers report online this month in Molecular Ecology. The same pigments that are essential for the corals’ color are also important for protecting the algae that live inside the corals, the team reports. Algae require some sunlight to survive, but too much light kills them. To protect the algae, which provide them with essential nutrients, the corals that are exposed to the most sunlight invest the sun’s energy into producing more pigment and thus appear brighter; this prevents too much sunlight from reaching the algae.