The only way he could cover his condition is to have most of the pigment removed.
His claim of Vitiligo was later confirmed by an autopsy and various doctor testimonies after he died.
Up until that point, many people didn't believe him and thought he hated his own race. His Brothers later came forward and confirmed that he has a autoimmune skin disease that would otherwise cause him to look like he was disfigured.
White people also get Vitiligo, it causes their beige skin to have white blotches like a leopard. In people with dark skin, the condition can leave them looking like an albino with bruises.