it's not important. I won't like someone more or less because of their hair colour but I generally prefer darker colours because the higher contrast to the skin looks less boring in my opinion. but that's just my personal taste and doesn't mean that I don't think blondes are attractive... ;)
I notice it, but I don't pay attention to it. The farthest my mind goes in regards to hair as far as looks are concerned is if the style is flattering on her and if the color is good on her. Some girls dye their hair and it just does not look appealing. The girls that dye their hair and you can't tell it isn't natural are the ones that are doing it right.