Tazria - Sheini
“Well, It’s All White Now… And Now It’s Tzaraas”*
The kohein will examine the person yet again and if the mark still hasn't worsened, he will declare the person clean. (The person must immerse himself and his clothes in a mikvah.) But if the discoloration has gotten bigger, the kohein will declare it tzaraas and the person is ritually unclean.
If, when the person first comes to show the spot, the kohein can see that the hair in the affected area is white or that there is a healthy patch within the affected area, it's obviously tzaraas. If the person has turned completely white, in every visible spot, that's not tzaraas and he's clean. (If a healthy spot appears among the discoloration, he's a metzora, but if it goes away, he's clean again.)
*(To the tune of “Jumping Jack Flash”)