The bi color parrot fish changes color when it gets older.They eat hard corals and algae.The coral is crushed into sand and ground with the algea to aid in digestion.They don't do well if they don't get a good supply in there diet.
Although they are considered to be herbivour, parrotfish eat a wide variety of reef organisms. Species such as Bolbometopon muricatum include coral polyp in their diet.