I would find out what the rules are. If it's just the teacher's opinion, then she'll just have to deal with it. And, it's not really a teacher's place to tell a student that they look trashy. Even if you walked in there looking like a hooker on the corner, as a teacher, she should be a little more appropriate with the way she tells you it's inappropriate dress. But, yeah I'd find out what the actual rule is, then go from there. If it's the rule, and, I don't see how it would be, then take the nail polish off or if you really want to protest, find out how you would go about changing the rules. If it's not a rule, then tell the teacher hey i'm sorry you don't like my nail polish, but, it's not against the rules, and, i'm not removing it. good luck with it.