In regards to the dinim of chatzitza by the tevillah of a Niddah the SA (Rema) in YD Siman 198 Sif 6 speaks about an interesting situation where a woman's hair was tied together by a Shin-Daled ...
What are the halachic issues involved in hair dyeing for women? Most importantly, does hair dye constitute a chatzitza for mikvah? Also: are there any communities that forbid hair dyeing altogether? ...