Halakhah zu Wajikra 13:6

And if you will ask - if so, what is that which is stated in the Torah (Leviticus 13:6), "and behold, the ailment dimmed [...] the priest shall render him pure"; your answer is that this is stated about the ailment dimming beyond the membrane of an egg. But with the membrane of an egg and above it, this is not [considered] dimming, as it is still included in the appearances of impurity. And that which is stated (Leviticus 13:6), "and the ailment did not spread in the skin, the priest shall render him pure," instructs that any time it did not spread at all and none of the other signs of impurity that we said developed - even though it did not dim, but rather stayed in its hue - since it did not spread, he is pure.