TT #269 · 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 allowing the two prescribed colors to combine even though their mottled blend is not itself a qualifying appearance.
Sifra — Vayikra 13, Midrash Sefer
English: Might the greenish and reddish appearances also fail to combine with one another? Scripture says, “and it shall be.”
Textual derivation
The greenish and reddish appearances do not qualify when blended into a mottled color, but the separate areas of the two qualifying shades may combine for the relevant measure.