Any ideas why ginger hair is attractive on a woman but not on a man? It just seems a bit unfair.

There is hardly any decent research on hair colour. Most hair research in on beards or chest hair, not hair on the head. Shame, as there is probably lots of interesting stuff still to learn.

Seen research before on hair color. Said, as far as male preference, men tend to prefer dark hair.
My own observations, blonde hair makes facial features stand out less. So the medium appealing face gets a little leeway. Simple contrast. But blondes aren't better. The nice looking dark haired girl will be really nice looking.
From an unscientific 20/20 tv show experiment, they had the same woman stand out on the street pretending to walk her dog. They counted how often men tried to interact with her as a blonde and as a brunette. The recorded more interactions as a blonde and concluded that "blondes have more fun". But they didn't account for the fact, by watching the show, that the woman when she was blonde acted more open and friendlier with the men as they passed by. Had more eye contact and smiled more. So the men talked to her more those times.

Good point. Also, some people probably die their hair darker or lighter because they want to be seen a certain way, or to better reflect their personalities. So maybe introverted blondes are more likely to die their hair brown than extroverted blondes.

I've been doing a bit of thinking about why ginger and blonde hair is attractive on women. It could be just that men like bright colours on women anywhere on their bodies, faces or hair kind of similar to how the females in many bird species are attracted to brightly coloured males.

Just take a look at the woman in this McDonald's ad.

https://www.youtube.com/watch?v=_UKLncvGxQ8

There's something incredibly attractive about those bright reds and yellows all over her. She looks so tasty and sweet like fruit. This makes me think about how often women and their attractiveness are likened to fruit: "Sweet 16"."Popping a girl's cherry". The metaphor of puberty for girls as ripening. The number of fruit scented hygiene and beauty products for women. There's even a popular brand of clothes for girls called "Pineapple". And leggings like these: http://img.ie/277bj.jpg

Conspicuousness or difference from the usual is probably attention-grabbing, yes. The thing with birds preferring bright colours, though, is that those colours mean something: red males are attractive because redness indicates a healthy immune system. It's possible that red hair in humans means the same thing, but I'm not so sure! The problem also is that red hair is rare, but it's not found the most attractive: blonde hair usually is. It's a complicated problem, which might be why researchers have tended to shy away from it.

Additionally, a few individuals likely kick the bucket their hair darker or lighter on the grounds that they need to be seen a certain route, or to better mirror their identities. So perhaps independent blondes are more prone to kick the bucket their hair cocoa than outgoing blondes.