Mishnà su Levitico 13:10

The signs of negaim are two which, in fact, are four. The bright spot (baheret) is bright white like snow; secondary to it is the sign as white as the lime of the Temple. The rising (se'et) is as white of the skin of an egg; secondary to it is the like white wool, the words of Rabbi Meir. But the sages say: the rising (se'et) is white wool and secondary to it is like the white of the skin of an egg.

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.

A bright spot the size of a split bean and there was nothing else, and then there appeared a bright spot of the size of half a split bean having two hairs, this one is declared unclean. Because they said: if the bright spot preceded the white hair he is unclean; if the white hair preceded the bright spot he is clean; and if it is doubtful he is unclean. Rabbi Joshua regards this as unsolvable.