Mishnà su Levitico 13:13

These four colors combine with each other to declare free [from uncleanness], to certify or to shut up. "To shut up" one who is at the end of the first week; "To declare free [from uncleanness]", one who is at the end of the second week. "To certify", one in which a discoloration or white hair arose, by the end of the first week, by the end of the second week or after it had been declared free [from uncleanness]. "To certify", when a spreading arose in it by the end of the first week, by the end of the second week or after it had been declared free [from uncleanness]. "To certify", when all one's skin turned white after it had been declared free from uncleanness; "To declare free from uncleanness’, when all one's skin turned white after the sign had been certified unclean or after it had been shut up. These are the colors of signs of negaim upon which depend all decisions concerning negaim.

There are [laws] that apply to white hair that do not apply to quick flesh, while others apply to quick flesh and not to white hair. White hair causes uncleanness in a boil and in a burn, whether growing together or dispersed, and whether encompassed or unencompassed. There are [laws] that apply to quick flesh, for quick flesh causes uncleanness in scalp baldness and in forehead baldness, whether it was turned or was not turned, it prevents the cleanness of one who is turned all white, and causes uncleanness whatever its color, and these do not apply to white hair.

If a nega broke out completely upon one who was unclean, he becomes clean; If the ends of his limbs reappeared, he becomes unclean until the bright spot is reduced to less than the size of a split bean. [If it broke out completely upon him] when he was clean, he becomes unclean; If the ends of his limbs reappeared, he remains unclean until his bright spot resumes its former size.