וְכִֽי־יִרְאֶ֨ה הַכֹּהֵ֜ן אֶת־נֶ֣גַע הַנֶּ֗תֶק וְהִנֵּ֤ה אֵין־מַרְאֵ֙הוּ֙ עָמֹ֣ק מִן־הָע֔וֹר וְשֵׂעָ֥ר שָׁחֹ֖ר אֵ֣ין בּ֑וֹ וְהִסְגִּ֧יר הַכֹּהֵ֛ן אֶת־נֶ֥גַע הַנֶּ֖תֶק שִׁבְעַ֥ת יָמִֽים׃
And if the priest look on the plague of the scall, and, behold, the appearance thereof be not deeper than the skin, and there be no black hair in it, then the priest shall shut up him that hath the plague of the scall seven days.
Mishnah Negaim
Yellow thin hair causes uncleanness whether it is clustered together or dispersed, whether it is encompassed or unencompassed, or whether it came after the scall or before it, the words of Rabbi Judah. Rabbi Shimon says: it causes uncleanness only when it came after the scall. Rabbi Shimon said: Is it not logical: if white hair, against which other hair affords no protection, causes uncleanness only when it comes after the nega, how much more should yellow thin hair, against which other hair does afford protection, cause uncleanness only when it comes after the scall? Rabbi Judah says: Whenever it was necessary to say, "it turns" Scripture says, "it turns." But the scall, since about it Scripture says, "there is no yellow hair in it," it causes uncleanness whether it came before or after it.