What is the factual difference between a Nega in the location of flesh and a Nega in the location of hair?
Rashi (citng the Beraisa of R. Yishmael - according to the interpretation of the Ramban): The sole sign of Tum'ah on the latter is two yellow hairs that grow in the location of the black hair that is still intact. 1
Ramban #1: The sign of Tum'ah on the former is two white hairs, on the latter, two yellow hairs, after a patch of black hair has fallen out, 2 which explains why it is called 'Nesek' 3
Ramban #2, Targum Onkelos and Targum Yonasan: The latter, like the former, requires a patch of white skin 4 with one of the four appearances (Se'eis, Baheres and their Toldos), only instead of two white hairs, the Siman Tum'ah of the latter is two yellow hairs.
Ramban #3 (based on the Tosefta 1:4): The latter, like the former, requires skin without hair, but they are not limited to the four appearances of white. It can be a white patch on black (skin of the head) or a black patch on white. 5
See Ramban's objection to this explanation. See also R; Chavel's footnotes, who equates Rashi's explanation with the third explanation of the Ramban (Refer to 13:30:1:4). However refer to 13:43:1:1.
It is not, however subject to the four appearances (Se'eis, Baheres and their Toldos)..
Which means 'fallen out'. See Oznayim la'Torah, who queries this from the fact that the Torah writes "Mar'eihu Amok min ha'Or" and elaborates at length.
Where the black hair has fallen out.
Ra'avad: The Tosefta implies that a changed appearance is needed, but the Sifra implies that it is not.
What is "u'Mar'eh ha'Nesek Amok min ha'Or" referring to?
Ramban #1: It refers to the yellow (bright-colored) hairs that look deeper than the skin. 1
Ramban #2: It refers to the Nesek that turned white after the black hair fell out. 2
Seeing as a Nesek is Tamei even if it appears equal to, and even higher than, the skin (See Torah Temimah), why does the Torah insert "ve'Hinei Mar'eihu Amok me'Or Besaro"?
Sifra: To teach us that it is only a Sim'an Tum'ah if, like the appearance od the Nesek, the hair falls out is only a Si'man Tum'ah if it falls out bi'Yedei Shamayim, but not if it is pulled out.
What are the three times "Se'or Tzahov" in the Parshah (here, in Pasuk 32 and in Pasuk 36 coming to teach us?.
Sifra: They preclude green, red and white hair 1 that appears, from the Din of Tum'as Nesakim.
See Torah Temimah, note 131.
What are the connotations of Se'or ... Dak"?
Sifra: It implies a thin and short hair.
What is the meaning of "Nesek Hu"?
Rashi and Seforno: It is the name of a plague. 1
Sifra" It implies that, if the hair falls out it is a Si'man Tum'ah, even if it does not resemble any of the four Mar'os Nega;im of Tum'as Basar. 2
Why does the Torah add the (otherwise superfluous) phrase "Tzara'as ha'Rosh O ha'Zakan"?
Sifra: To teach us that Baheres (and Se'eis) do not apply to the head or the beard, only Nesek.
What are the two times "Nesek Hu" coming o preclude?
Sifra: It precludes 1. two hairs falling out in a location of Baheres, which is not a Si'man Tum'ah; 2. the various appearances of Tum'ah in the location of a Baheres, which are not a Si'man Tum'ah in the location of a Nesek.
