Mishnà su Levitico 13:15

A bright spot in which there was white hair and then it broke out covering his entire skin, even though the white hair remained in its place, he is clean. A bright spot in which there was a spreading and then it broke out covering his entire skin, he is clean. But in all of these cases if [even] the ends of the his limbs reappeared [in their natural color], he is unclean. If it broke out covering a part of his skin he is unclean; If it broke out covering all his skin he is clean.