Light and Dark in manga

Something I've noticed, mostly in shoujo manga, is a predominance of light vs. dark in love triangles.  I mean, typically, the romantic set-up of a shoujo manga will go something like this: the main character girl will have a crush on the one boy who is nice if a little out of her league, and he almost always has light-colored hair.  And then there's the other boy who pisses her off, and vice versa, but he starts to warm up to her, and her to him, and this boy almost always has dark-colored hair.  I've seen this in Kitchen Princess, Boys Over Flowers, Peach Girl, Shugo Chara!, and to a certain degree in Fushigiboshi no Futago Hime.  And I know that there are more that I either haven't read or just aren't coming to mind.

What bugs me about this set-up, though, is that in every example I've seen, the dark-haired boy gets the girl!  Not that this is a bad thing, but when it happens over and over again, and is done poorly, it starts to piss me off.  I'd say Boys Over Flowers and Peach Girl are good versions of this, but I could be biased as I read those before I noticed the trend.  Kitchen Princess is where I started noticing this, and Shugo Chara is where it started to bother me, mostly because I do not like Amuto in the least, and unfortunately for me, the forces of shoujo seems to say it will be so.  (Granted, I'm only following the US release, and I'm about twenty episodes behind the anime.)  As they say, knowing the tropes is not a good thing in some cases.