I don't have a hair colour preference, and with most women/girls nowadays, whatever colour hair they haven't probably isn't their natural colour anyway. Red-heads/gingers, blondes, brunettes, raven locks, long hair, short hair, afro hair, curly hair, straight hair and even no hair. As long as it's not in my teeth, I'm okay with it.
Games: redheads with green eyes and not too many freckles, if possible (good luck with that). Barring that, curly blondes
IRL: Brunettes
But frankly, hair color is such a minor detail.