Am I allowed to see my wife’s hair
When she is tahor it is permitted, and when she is a nida it depends. If she usually walks around the house with her hair covered, then it is considered a makom mechusa and he should not look at her hair, and if she usually walks around the house with her hair uncovered then it is controversial. R’ Moshe zt”l held that since she walks around the house this way, (although it is preferred not to) it isn’t considered a makom mechusa and he may look, however other poskim say that it is still considered a makom mechusa and that he shouldn’t look. See sources.
Igros Moshe Y:D 2-72, Shiurei Shevet Halevi Y:D 196-2 sikum 2, Chut Shani 196-9, OhelYackov Y:D 195-7 (4), Mareh Cohen pg. 82.