Parashas Metzora · Passuk 15:03
Chabad.org — English translation + Rashi
Torah Temima points to Toras Kohanim.
English: “His impurity is in his discharge” — he becomes tamei through white [discharge] and does not become tamei through red.
Color requirement
Chazal limit the impurity of the male zav to a white discharge; a red discharge does not create the status of zav.