Midrasch zu Wajikra 13:16

1) (Vayikra 13:16) ("If the healthy flesh recede and it return to white, then he shall come to the Cohein.") "If the healthy flesh recede and it return to white": This comes to teach us that if limb tips were revealed and were then again covered (by white), he is tahor. When is it derived that this is so even with a hundred repetitions of the same? From "Or if it return" rather than (simply) "If it return."

2) "and it return to white": (even to the appearance of bohak (white scurf). For I would say that since in the beginning it is a sign of tumah (i.e., it impedes "complete blossoming," which would render him tahor), then in the end (with later repetitions or the same) it would remain the same, it is, therefore, written "and it return to white" (even) to the appearance of bohak.