Why rhodophyta exhibit red colour ?

Rhodophyta are commonly called as red algae because of the predominance of the red pigment (r – phycoerythrin) in their body. They occur in both well lighted regions close to the surface of water and also at great depths in ocean where relatively little light penetrates. They exhibit a red colour because the wavelengths of light that are absorbed by chlorophyll are blue light absorbed by phycoerythrin and it looses some of the energy as red light.