TT #113 · 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 requiring both white hair and healthy flesh to be within the qualifying se'eis.
Sifra — Vayikra 13, Midrash Sefer
English: The white hair and healthy flesh must be encompassed by the se'eith.
Textual derivation
The white-hair sign and the healthy-flesh patch must both lie within the qualifying se'eis; merely being adjacent to it is insufficient.