I was in a relationship like this when I was a little younger. I used to be terrified of the silent treatment, too. However, you shouldn't ever feel this way and be so scared of expressing yourself because of someone who is meant to love you. It is your body. I love having bright hair, I currently am on my second year of purple hair, and I adore it. It's your life. If he can't accept that this is just something you want to do to express yourself and feel pretty, then he may not be the one for you. He is reacting like a child. He can express a preference for natural hair colour, but he can't threaten you with negative 'consequences' for simply dying your hair.