TT #203 · Parshas Tazria · Aliyah 5 · Passuk 32
English: The priest shall examine the netek on the seventh day. If it has not spread, there is no yellow hair in it, and its appearance is not deeper than the skin,
Chabad.org — Chumash, English translation + Rashi for Vayikra 13:32
Torah Temimah cites Sifra (Toras Kohanim) for the significance of whether yellow hair preceded the netek.
Sifra — Vayikra 13, Midrash Sefer
English: Rabbi Judah reads “there was no hair in it” precisely: if yellow hair had already appeared before the netek developed, the case is impure.
Textual derivation
For Rabbi Judah, chronology matters: yellow hair that preceded the netek renders the case impure, unlike hair that appears only after the netek.