Oidasaretara, Nani ka Toumaku Ikimashite

Alec, the youngest brother of the renouned Mornort family, has purple hair and purple eyes. His parents were uncomfortable with his coloring, which no human is supposed to be born with, until one day he was banished from the family home. At a loss, Alec happens to meet two girls who seemed like adventurers. At their suggestion, Alec changes the color of his hair and eyes, and enrolls in the Academy of Heroes without telling anyone about his true identity. Alec's life at the academy is a lively one, but there is a secret legend about the color of his hair and eyes that even he doesn't know... (Source: Alphapolis, translated)