I like pink hair in theory, although I've never dated a girl with pink hair. It seems like too much work, but then again so does fake "natural" colors, and girls do that a lot already. At least pink is new and throws out the pretense that they're trying to pass it off as natural.
I like natural hair color but I find myself attracted to girls with dark red hair. For example Ariana Grande, I think she is a cute girl that really pulls it off. Any other color seems odd to me unless they can pull it off, but I don't think I would date a girl with blue or purple hair even if it looked good.