With or without dark rootsI understand that this is somewhat ambiguous, but stay with me. If you'd asked me several months ago about the blonde hair with dark roots colour trend I would have told you it has had it's day. But it hasn't, and it's hung around accordingly, but I do still believe that it is coming to an end. Thus if you were to opt to change your hair colour to white blonde / platinum blonde in the near future (say, prior to the middle of 2011) I think you'd be safe to do opt for dark roots.
That said: if it's an option, forgo the dark roots and opt for a full head of platinum / white blonde hair instead. The overall impact of platinum blonde hair will be diminished should you opt for dark roots and wear it with an up do. You can get a good sense of this dimishing affect by comparing the following picture of model Siri Tollerod with a picture of her from J. Crew's catalogue above.
If you're after more of a rock chic look, however, I can recommend one person you must keep your eye on for inspiration: Australian model Kate Peck. She has the look pegged, and pairs a dramatic hair colour with an equally dramatic hair cut to really set herself apart on the catwalk.
While not truly platinum / white blonde, our feature on 5 ways to style peroxide blonde should also lend some inspiration to those seeking the hair colour for themselves. That hair styling inspiration feature specifically looks at styling the hair colour when cut with a fringe.