I would disagree, hair algae can take many colors, including red, Grey or white. It depends on the type of chlorophyll and it's pigmentation. Though admittedly the term hair algae can refer to hundreds of different forms of algae. It's almost impossible to label the types of algae without a microscope.I would check the top thread for "Guitars algae" etc on Algae section. The shape looks like both hair and Staghorn but hair is green and staghorn can be several colors.
They list causes and cures for each in that list.