Removing white hairs:
It is [Biblically] forbidden for a man to remove even a single white hair from amongst black hairs [so he does not appear old] due to the prohibition of “Lo Yilbash Gever Simlas Isha.” [One who does so is liable for lashes. This applies to the hair of the head or beard. This applies even if one has many white hairs and only removes one white hair from among the many. If however one removes the hair for non-beauty purposes, then he is not liable for Lo Yilbash.]
On Shabbos: On Shabbos, one who gathers white [hairs] from amongst black hairs so he does not appear old, even if he removes one hair, is liable [for a sin offering due to the Melacha of Gozez]. This is in addition to the prohibition against “a man wearing the garment of a woman.” [If however, one removes the hair for non-beauty purposes, then he is not liable for Lo Yilbash, and is also not liable for Gozez unless he removes two hairs.]
May one remove white hair from black hairs for non-beauty purposes?
May one remove white hairs from amongst black hairs if the custom in his country is also for men to do so?
May one remove white hairs from amongst black if he feels ashamed of walking around with white hairs?
May one cut his white hairs together with his black hairs?
May one comb his hair, or play with his hair, if it may cause white hairs to come out?
May one have a gentile remove the white hairs from the black hairs?
May one hide a white hair amongst black hairs?
May one trim a white hair from amongst black hairs?
May one remove white hairs from his eyebrow?
May one remove white hairs from his nose canal?
May one remove a black hair from amongst white hairs?
 Michaber O.C. 340/1; Y.D. 182/6; Admur 340/1; Shabbos 94b; Makos 20b
 Rambam Avoda Zara 10; Beis Yosef 182 that one who does so is liable; Beir Hagoleh
Other opinions: Some Poskim rule that removing a white hair is only Rabbinically forbidden. [Ravad, on Rambam ibid; Shoel Umeishiv Kama 1/210; See Darkei Teshuvah 182/17]
 Admur ibid; Rashi Shabbos ibid; Rivan Shabbos ibid; See Ketzos Hashulchan 143 footnote 3; Igros Kodesh 1/10
 This verse is translated in Targum as “A man may not adorn himself with the adornments of women.” [Admur ibid]
 Rambam ibid; Beis Yosef 182
 Beis Yosef 182 that the hair of the head and beard is included in the Biblical prohibition
 Beis Yosef 182
Other opinions: Some Poskim rule that removing a white hair is only forbidden when all the white hairs are removed. [Ravad, brought in Beis Yosef ibid]
 See Q&A
 Admur ibid; Michaber O.C. ibid; Shabbos ibid
 Ketzos Hashulchan ibid
 Implication of Admur ibid and Rishonim ibid; Ketzos Hashulchan ibid based on Admur ibid and Michaber Y.D. 182/4 and Tosafus Shabbos 50b
 Shevet Halevi 3/111; Lehorors Nasan 2/70; See Igros Kodesh 6/268, [printed in Shulchan Menachem 4/133]
 Ketzos Hashulchan ibid based on Admur ibid and Michaber Y.D. 182/4 and Tosafus Shabbos 50b; Shoel Umeishiv Kama 1/210; Beir Moshe 8/8-6
 Mahariy Ashkenazi 19; See Divrei Chaim 2/62
 Divrei Chaim 2/62; See Darkei Teshuvah 186/17; Beir Sarim 6/60
 The reason: As the prohibition only applies when one removes the hairs due to beauty purposes.
 Halachos Ketanos 2/258; Agua Beahalecha p. 58, brought in Darkei Teshuvah 182/16
 Maharam Shick Y.D. 172
 Maharsham 2/243
 Kerem Shlomo 20-4; Shevet Hakehasi 2/257; Beri Sarim 60/7; Chayeh Halevi 6/127-3
 See Ohalei Yaakov p. 330; Shevet Hakehasi 6/307
 See Avnei Yashpa 6/118; Ohel Yaakov p. 331
 See Shevet Hakehasi 1/231; Ohel Yaakov p. 331
 Shevet Hakehasi 6/307; See Darkei Teshuvah 182/17; Ohel Yaakov p. 327