Are there any blue seaweeds?
ABlue seaweeds are conspicuous by their absence, though there may be one exception, depending on the angle from which you view it. Rainbow wrack, a common British rockpool species, has an opalescent quality that can make the plant appear blue, green or pink. The colours are produced not by photosynthetic pigments, but by microscopic, oil-based structures that scatter light in all directions, much like real opals do. This opalescence may increase light absorption when the seaweed is submerged. At low tide, the plant switches off the effect, perhaps to protect itself from the full glare of the sun.
Showing its true colours?