May one dye his hair in an area that it is common practice for men to do so?
Some Poskim rule that the entire prohibition stated above against men dying hair is only in areas that men are not accustomed to dye their hair. However, in areas that men are accustomed to dye their hair then it is permitted for men to dye it. Other Poskim however rule the dyeing prohibition applies in all cases, and it is hence forbidden for men to dye their hair even in areas that men are accustomed to do so. Statistics in the USA show that approximately 2-7% of the population of men dye their hair. The Rebbe states that today, all men, even married want to look younger and consequently dye their hair. Nevertheless, the Rebbe concluded stringently in this matter.
 See Igros Kodesh 6/268, [printed in Shulchan Menachem 4/133]; Ohel Yaakov 81
Background: There are three levels in Beged Isha: a) A matter which is Biblically considered Beged Isha, such as armor. B) Matters which their inherent purpose is for beauty for a woman. C) Matters which are simply accustomed only by women. Level a) can never change irrelevant of the custom, level c) is dependent on the custom, however level b) can be viewed both ways. Dyeing hair is considered like b) and hence is subject to argument in whether its law changes upon the change of custom. [Igros Kodesh ibid]
 Imrei Yaakov 2/18 [Rav Yaakov Shtern]; Mesores Moshe of Igros Moshe p. 248; Leaning opinion of Rebbe in Igros Kodesh ibid however he does not conclude this way; See Ohel Yaakov 79 footnote 109
 The reason: As some of the prohibitions of Beged Isha only apply when men are not accustomed to perform the actions. [Michaber 182/1 regarding shaving] This possibly applies even if it is only common for gentiles to do so. [Perisha 182, brought in Rav Akiva Eiger 182; Igros Kodesh ibid] Now, the dyeing of hair falls under category b) brought above which seemingly is subject to change based on custom. [Igros Kodesh ibid]
 Setimas Haposkim; Shevet Halevi 3/2
 The reason: As dyeing hair is an inherent practice of women for purposes of beauty and can never be changed irrelevant of custom.
 See: http://articles.latimes.com/2012/jan/29/image/la-ig-mens-hair-color-20120129
 Igros Kodesh 8/155, [printed in Shulchan Menachem 4/136]; Igros Kodesh 6/268, [printed in Shulchan Menachem 4/133] the Rebbe leans to be lenient although than concludes that all above is “Lehalacha but not Lemaaseh in any way, and Bepoel the Achronim already gave their ruling”