The gemarah (shabbos 94b) says that the normal shiur to be chayav for plucking hairs is two. However, this only applies to mono colored hairs; when it comes to plucking white hairs from black hairs, (so that he should look younger), even on one he is chayav for tolesh (gozez), as this is a shiur choshuv.
Why does the gemarah only talk about being chayav for tolesh; seemingly this should also fall under the category of borer? (Maybe it is going according to the shittah (biur halachah) that you're not chayav for borer until you remove all of the pesoles?)
Asher Weinberger
Shalom Rav!
According to your suggestion, if one pulls out the only white hair (what would be the point of pulling it out if it wasn't the only one?), one ought to be Chayav because of Borer, in which case, your suggested answer will not work.
It seems to me that Borer does not apply here, since one is neither selecting the good from the bad nor the bad from the good. This is because one wants neither the white hair nor the black ones. One is removing the hair because he finds it offensive, not in order to use it or the remaining hairs, and this has nothing to do with Borer.
Besides, I wonder whether Borer applies to Mechubar (something attached) altogether, as there seems to be no case in the Gemara, Rambam, or Shulchan Aruch of Borer with Mechubar. It therefore seems that picking from what is attached falls exclusively under the category of detaching, and that is therefore what the Gemara calls it.
B'Virchas Kol Tuv,
Eliezer Chrysler