How do I kindly change my girlfriends opinion?

My girlfriend is a blonde and wants to go darker and she wants to dye her hair either red or blue and I person don't like either I love her the way she is right now I would never break up with her over this change or make me loe her any less but I just don't like it I'm sorry if I sound like a bad boyfriend by saying this but I would just like too gently chang her mind without being a jerk
How do I kindly change my girlfriends opinion?
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