Be honest!!! don't hide things later are going to come out and it's gonna be worst! If you say she loves you so so much she wouln't have to get mad.. even she would change her new hair again. But that's not positive either, you should not change anyone for you, let her be. You should love her as she is.. if you don't then you don't love her as you think.
Anyway, tell her, even she doesn't react well.. you should be free to tell things you don't like in your relationship and not be afraid don't you think??