She looks completely dfferent as a blond than she does as a brunette. Also, the lighting in the pictures is different.
As a brunette her eyes "pop," but as a blond she looks like a natural Scandanavian.
It's unusual for a natural brunette to really carry of the blonde look. For example, Nikki's a natural brunette, and she is a stunning beauty as a brunette. As a blonde, she looks harsh and shopworn. I was shocked when I saw her for the first time in the movie, because Rosalie is supposed to be one of the most beuatful women in the world, and I didn't see that at all.
I wish they could have let Nikki be a brunette--but that would be total out of character.