TT #268 · Parshas Tazria · Aliyah 7 · Passuk 49
English: and the lesion is greenish or reddish in the garment, leather, warp or woof, or any leather article, it is a lesion of tzaraas and shall be shown to the priest.
Torah Temimah cites Sifra (Toras Kohanim) for excluding mottled mixtures of the greenish and reddish appearances.
Sifra — Vayikra 13, Midrash Sefer
English: The greenish and reddish categories do not become impure when the appearance is mottled.
Textual derivation
The greenish and reddish appearances qualify separately, but a mottled blend of the two is not itself one of the qualifying colors.