i like a solid color just as much as something that varies; but if the color is really contrasting or unnatural (pink, green, purple etc) I think lots of girls can't pull it off. that's not to say everyone can't just it looks strange on most and very good on some. if the highlight is a natural looking color (browns, blondes etc) then it can add depth and substance to the hair. sort of like different amounts of light shining through water.
one girl I know has a very dark blond hair that is long and it's a deep brunette in the last three or four inches; it looks good. another has a pixie cut (I think that is what they called) and she has had green highlights and purple highlights (not at the same time) and it also looked good.
then there are also girls who have gotten blue highlights or pink highlights and it looks ridiculous.