I'm a brunette. In my experience lots of guys go for brunettes. In fact I think its slightly more common than going for blondes, at least, in the UK that is the case. People associate blondes with being either stuck up or stupid. But I have some pretty blonde friends who get a lot of attention, though people don't seem to want to date them, that is bar, this one friend who is at Oxford University, very witty and intelligent to go with it.
I think most guys don't care. Its more about the general appearance.
If the girl is really pretty, it will be universal. My mum was gorgeous when she was my age, and a curly haired brunette, with some curves but very very slim. My dad went for stick insect blondes. They just celebrated their 25th wedding anniversary.