TT #114 · 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 excluding a boil and a bright spot from the qualifying se'eis.
Sifra — Vayikra 13, Midrash Sefer
English: The qualifying appearance must be se'eis; a boil and a bright spot do not qualify as se'eis.
Textual derivation
A boil and a bright spot are excluded from the definition here; they cannot substitute for the qualifying se'eis appearance.