Phycobilin

Any of a group of water-soluble proteinaceous pigments that occur in red algae and cyanobacteria. Especially good at absobing blue light. It is often said that this enables those organisms which contain them to grow at deeper depths in the water, but there is no scientific evidence that this is true. Red algae, for example, can grow at depths of up to 260 meters, but then so do some green algae.