Rashi on Leviticus 13:6/רש"י על ויקרא י״ג:ו׳

1כֵּהֶה means it has become paler than its former color — consequently if it remains in its color or if it has spread he is unclean.

2מספחת — This is the name of a clean leprous disease.

3וכבס את בגדיו וטהר AND HE SHALL WASH HIS GARMENTS AND BE CLEAN — Since he required shutting up he was termed (was regarded as coming under the term) “unclean” (although it now transpires that he was clean), and he must undergo immersion in a ritual bath.