Depends on lots of factors. Here are a few.
If the diamond has floresence, it might face up a bit whiter, allowing you a higher color.
Color really depends on person. I didn't like the look of higher colors, so I only looked at E & D colored stones (and got an E because I couldn't tell the difference). You might think G looks totally white. Some people might think I is white. So, do some searching and find the right color to your eye, or more importantly, her eye.
Diamonds with lots of sparkle can hide things like color and inclusions. Get a well cut stone and it should be beautiful no matter what color.
People always talk about color, then talk about diamond "facing up" white. While I'm no expert on this, I would assume there's a certain amount of play a diamond has. Since diamonds are graded upside down in regards to color, they could face up slightly different. Would love an expert to comment on this.
Hope these variables help your decision.