I personal like any kind of hair, but if i really have to choice. It would be Brunettes, most guys might say Blondes but i don't really find hair 100% attractive, but if a woman didn't have hair it's still a big turn off.
Having different color hair is not a big deal with me, as long as it's not crazy like Blue and green mixed, but for some reason i don't mind girls having their hair dyed.
I think the biggest turn on for me is a girl with Red/Pink hair with tattoos, i don't really understand why but they look cute. But i am really happy with my one and only girl