Mishnah Negaim 10:1: Netakim [diseased patches on the head or beard] make impure after two weeks [maximum] and through two signs: Thin yellow hair or spreading. Thin yellow hair [means] diseased and short. [These are] the words of Rabbi Akiva. Rabbi Yochanan ben Nuri says: Even if long. Rabbi Yochanan ben Nuri said: What does the phrase that they say [mean], "This stick is thin" [or] "This reed is thin?" [Does it mean] thin, diseased and short or thin, diseased and long? Rabbi Akiva said to him: Before we learn from the stick, let us learn from the hair. [If one says,] "The hair of so-and-so is thin," [he means] "Thin, diseased and short," not "Thin, diseased and long."

הַנְּתָקִים מִטַּמְּאִין בִּשְׁנֵי שָׁבוּעוֹת, וּבִשְׁנֵי סִימָנִים, בְּשֵׂעָר צָהֹב דַּק וּבְפִשְׂיוֹן. בְּשֵׂעָר צָהֹב דַּק, לָקוּי קָצָר, דִּבְרֵי רַבִּי עֲקִיבָא. רַבִּי יוֹחָנָן בֶּן נוּרִי אוֹמֵר, אֲפִלּוּ אָרֹךְ. אָמַר רַבִּי יוֹחָנָן בֶּן נוּרִי, מַה הַלָּשׁוֹן אוֹמְרִים, דַּק מַקֵּל זֶה, דַּק קָנֶה זֶה, דַּק לָקוּי קָצָר, אוֹ דַק לָקוּי אָרֹךְ. אָמַר לוֹ רַבִּי עֲקִיבָא, עַד שֶׁאָנוּ לְמֵדִים מִן הַקָּנֶה, נִלְמַד מִן הַשֵּׂעָר. דַּק שְׂעָרוֹ שֶׁל פְּלוֹנִי, דַּק לָקוּי קָצָר, לֹא דַק לָקוּי אָרֹךְ:

Mishnah Negaim 10:2: Thin yellow hair makes impure [whether it is] concentrated or spread out, [entirely] surrounded [by the Netek] or not [entirely] surrounded, changed [to yellow by the Netek] or not changed. These are the words of Rabbi Yehuda. Rabbi Shimon says: It only makes impure if changed [by the Netek]. Rabbi Shimon said: And this is logical; just as white hair, from which another [non-white] hair does not save [his purity status], only makes impure if changed [by the Netek], thin yellow hair, from which another [non-yellow] hair does save [his purity status], is it not logical that it should only make impure if changed?! Rabbi Yehuda says: Anywhere [in the Torah] where it should say [it needs to be] changed, it said [it needs to be] changed. But the Netek, of which it is said, (Leviticus 13:32) "It did not have in it yellow hair," makes him impure whether changed or not changed.

שֵׂעָר צָהֹב דַּק מְטַמֵּא מְכֻנָּס, וּמְפֻזָּר, וּמְבֻצָּר, וְשֶׁלֹּא מְבֻצָּר, הָפוּךְ, וְשֶׁלֹּא הָפוּךְ, דִּבְרֵי רַבִּי יְהוּדָה. רַבִּי שִׁמְעוֹן אוֹמֵר, אֵינוֹ מְטַמֵּא אֶלָּא הָפוּךְ. אָמַר רַבִּי שִׁמְעוֹן, וְדִין הוּא, מָה אִם שֵׂעָר לָבָן, שֶׁאֵין שֵׂעָר אַחֵר מַצִּיל מִיָּדוֹ, אֵינוֹ מְטַמֵּא אֶלָּא הָפוּךְ. שֵׂעָר צָהֹב דַּק שֶׁשֵּׂעָר אַחֵר מַצִּיל מִיָּדוֹ, אֵינוֹ דִין שֶׁלֹּא יְטַמֵּא אֶלָּא הָפוּךְ. רַבִּי יְהוּדָה אוֹמֵר, כָּל מָקוֹם שֶׁצָּרִיךְ לוֹמַר הָפוּךְ, אָמַר הָפוּךְ. אֲבָל הַנֶּתֶק שֶׁנֶּאֱמַר בּוֹ (ויקרא יג) וְלֹא הָיָה בוֹ שֵׂעָר צָהֹב, מְטַמֵּא הָפוּךְ וְשֶׁלֹּא הָפוּךְ: