TT #193 · Parshas Tazria · Aliyah 5 · Passuk 30
English: the priest shall examine the affliction. If its appearance is deeper than the skin and it contains thin yellow hair, the priest shall pronounce him unclean; it is a netek, tzaraas of the head or beard.
Chabad.org — Chumash, English translation + Rashi for Vayikra 13:30
Torah Temimah cites Sifra (Toras Kohanim) for the rule that netakim do not create a fifth skin-affliction appearance.
Sifra — Vayikra 13, Midrash Sefer
English: “It is a netek”—might this add a fifth qualifying appearance to the four appearances of ordinary skin lesions? The verse identifies it as a netek, a distinct category with its own signs, rather than a fifth shade.
Textual derivation
The Torah’s separate netek category does not add another shade to the four qualifying appearances of ordinary skin lesions; netakim are governed by their own distinct signs and rules.