Both black and white rhinoceroses are actually. gray. Their differences come from their lip shape as a result of their diet. White rhinos have square lips and graze on grasses, while black rhinos have a pointed upper lip to pick leaves and fruits from trees. White rhinos have two horns, one of which is significantly longer than the other. Their horns grow as much as three inches a year and sometimes even grow up to five feet long. Female rhinos use their horn to protect their young, while males use theirs to fight off predators.