The school has a rule that if a student’s natural hair is brown it needs to be dyed black.
「地毛が茶髪の生徒に対して髪を黒く染めるように強要する校則はブラック校則だ。」
“The school has a rule, called the black hair rule, that if a student’s natural hair is brown it needs to be dyed black.”
校則 - school rule
地毛 - natural hair
茶髪 - brown hair
生徒に対して - in regards to students
黒く染める - dye black
強要する - force to/make
「髪だけで校則を破ったことがある。」
“I’ve broken the rules before just because of my hair.”
「高校のとき、メイク禁止校則があった。」
“There was a rule at my high school that forbade make-up.”