I'd probably look at the one on the right first, because of how distracting her hair color was.. It would spark initial attraction to the difference of what I would normally expect for haircolor; however, I'd be more willing to settle down with the picture on the left because it seems more natural. I'm of the mindset that appreciates natural beauty over modified beauty.
The blond would get noticed first yes but not because it was attractive. Bright colors simply pop out from their surroundings more. It's the same principle behind why roadside construction workers wear neon vests. Bright colors get you noticed, but not necessarily because they're more attractive. Darker colors blend with their surroundings more.
No, the brunette would catch my eye first. Brunettes are hot! Blondes.. eh can be but not as much. Even if its the same girl and her hair was natural brunette and one day turned into natural blond hair. I would prefer the brunette 100% of the time.
This is a question of rarity, I think, since I find dark hair men more desirable to me since I'm Norwegian blond, so the differences seem to be more appealing. I suppose it's the same for men. Then again, blond hair lights up the room, so I understand why men get bigger erections for blondes.
a hot girl is a hot girl. hair color doesn't matter