The members of Rhodophyceae algae are red in colour even though they have both chlorophyll a&b. This is due to the presence of a pigment called
Phycoerythrin
The members of Rhodophyceae algae have both chlorophyll a&b but they also contain the red colored pigment, phycoerythrin, which in turn causes red color to reflect back in the visible range when light shines on these algae.