Mischna zu Wajikra 13:6

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.