As far as I know, nail polish has to be removed before going to Mikvah; while hair dye and eyebrow tinting are ok… I am wondering how it is different, since it seems to have the same permanance. Can you kindly explain?
The difference between the two is that hair dye is very thin and only considered coloring. When you feel the hair you are not going to feel the thickness of the dye on it. Therefore it is merely considered coloring, and “coloring” is not considered a chatzitza. Nail polish on the other hand is thicker and leaves a layer of polish on the nail, i.e. when it peels you can feel the difference, therefore it is considered a chatzitza and has to be removed.
As a side point, this is in retrospect, however before going to the mikvah you should try to remove all dyes etc. even if it isn’t technically a chatzitza.
Y:D 198-17, Chut Shani Nidah 198- pg. 309, Rema ibid -1, L’torah U’lhorah 7 pg. 27, Ohel Sara vol. 2 8-3.