Is nail polish considered a Chatzitza for washing hands for bread and in the morning?
Women who are accustomed to dye their hands for beauty purposes, and the like, the dye is not considered an interval [between the water and the hand] and the washing is valid. This applies even if there is an actual layer of paint on the hand [i.e. Mamashus], and not only a mere color, so long as it only covers minority of the hand. [Thus, nail polish is not considered a Chatzitza for women. The above, however, is only true regarding washing hands for bread or in the morning, however, regarding immersing in a Mikveh with nail polish, the matter is disputed in Poskim.]
Nail polish is not considered a Chatzitza for washing hands.
If the nail polish began rubbing off one of the nails, is it considered a Chatzitza?
If the nail polish has begun coming off to the point that it is common for women to be particular to either remove it or re-polish it, then it is considered a Chatzitza. This applies even towards a single nail.
 Admur 161:5; Michaber 161:2; Rashba Toras Habayis Haruch 7:7; Rosh Mikvaos 27
 Admur ibid; M”A 161:3
 See Michaber Y.D. 198:15 that dry ink is a Chatzitza and 198:17 that the paint on the hands of women is not a Chatzitza, which would imply that a woman may immerse with nail polish, even though the polish has Mamashus; So is also the implication of Admur ibid who does not differentiate in this matter as he does by other laws of Chatzitza; So also rules Binas Adam 119:14; Pnei Aryeh 6; Keren Ledavid 45; Taharas Mayim 70:2 regarding lipstick. However, the Rashba in Shaar Hatevila and Shach 198:21 brings two reasons as for why paint of a women is not a Chatzitza and according to the second reason it is not Chotzeitz because the dye has no Mamashus. This implies that if it has Mamashus then it would be Chotzeitz. So understands the Sidrei Taharah 198:33; See Shiureiy Shevet Halevi 198:17 [p. 324] that from the letter of the law is not Chatzitza although the custom is to remove; Taharah Kehalacha 19:45 that according to Admur and many Poskim its not a Chatzitza, and that so is ruling from letter of law
 Shiureiy Shevet Halevi 198:17 [p. 324]; Taharah Kehalacha 19:45; Piskeiy Teshuvos 161 footnote 4