Can I be fired for not changing my hair color?

Yesterday I walked into work and one of my coworkers had notified me that the Manager of the store was in today and had just sent a girl home due to her hair color. (The other girl's hair was pink) I felt that I didn't need to worry, mine was a pretty natural shade. I began to work and not even 5 minutes of being there the Store manager was telling me that I had to clock out and leave because of my hair color. They are cracking down more on the dress code, but when they notified us of that I asked my hiring manager if my hair color was fine and he said it was. The store manager has seen my hair color many times, and has never had a problem with it before. I have not changed my hair color since I've started working there, just redyed it the same color. The store manager says I have a week to fix it or I will be fired. Can he do that?