What can my school do if I don't change my hair?

This is my freshman year of high school. I've had a lot of friends that go to this school with blue or green hair and no one said anything to them. I even went to this school for summer school with blue hair and purple hair and no one said anything to me. When the school year started, I had pink hair. NOW LET ME TELL YOU. I went through a lot of **** and lost a **** ton of hair to get it pink. My hair was long and pretty, and now it's just above my shoulders. I hate it so much. I miss my long hair. But anyways. First day of school, no one said anything, teachers were even complimenting me on my hair. But the second day, an administrator stops me in the hall. She sends me home and tells me to dye it a natural color. I dyed it black, but it was a really cheap black so it faded really fast. I was sick of looking like a little emo ***** so I dyed purple over that, and the school threatened to write me up for 'defiance', but since I was polite they just told me to dye over it. But now I'm thinking about it, and I'm really mad. I'm about to cut my hair into a faux hawk. And I want to dye it bright fire truck red. What can they do if I don't change it this time? I know they can suspend me and give me detention but I really don't care. What else can they do? Cut it all off? Dye it for me?