Let us assess the situation. You would prefer to wear kilts. Your supervisor says, "No." and cannot offer a good reason. You have very few options. A lawsuit is out. You would lose - employers can determine their own dress codes. Recent court rulings have confirmed this. Your approach should be to volunteer to assist in development of the dress code and make sure it states that diversity in cultural dress should be leveraged. then you can use the company's stated policy aginst her.