13 the priest is to examine them, and if the disease has covered their whole body, he shall pronounce them clean. Since it has all turned white, they are clean.

Read Leviticus 13:13 Using Other Translations

Then the priest shall consider: and, behold, if the leprosy have covered all his flesh, he shall pronounce him clean that hath the plague: it is all turned white: he is clean.
then the priest shall look, and if the leprous disease has covered all his body, he shall pronounce him clean of the disease; it has all turned white, and he is clean.
When the priest examines the infected person and finds that the disease covers the entire body, he will pronounce the person ceremonially clean. Since the skin has turned completely white, the person is clean.