Years ago I taught in a chassidish hs in Bp. I was your very nice frum bais yaakov girl who dressed very tzanua...
However, this school made me wear beige 80 deniere tights, and wear my hair in a pony when it was longer than shoulder length.
I understood that this was their standard but honestly I felt it was very dishonest. Many times I would meet students out of school when I was dressed my regular way, so they knew it was all a game. My students really liked me and tried to copy the by girls so I could see why the school was scared but I thought it was a little close minded of the school to be so scared to let obviously frum by girls who did not belong to this specicific chasdidus wear their black tights!!
It also didn’t help that I was in shidduchim and people who would see me walking in bp (to and from school) thought I flipped out and would give information that I dressed chasdidish ( I was not chasdidish!)