TT #112 · Parshas Tazria · Aliyah 2 · Passuk 10
English: The kohen shall look [at it]. And, behold! there is a white se'eith on the skin, and either it has turned the hair white, or there is healthy, live flesh in the se'eith.
Chabad.org — Chumash, English translation + Rashi for Vayikra 13:10
Torah Temimah cites Sifra (Toras Kohanim) for the distinction between healthy flesh and a boil or bright spot.
Sifra — Vayikra 13, Midrash Sefer
English: Healthy flesh excludes a boil and a bright spot.
Textual derivation
The sign must be genuine healthy flesh; a boil or a bright spot is not counted as the required healthy-flesh patch.