Hello! I am thinking of getting my medium blonde hair dyed to a platinum blonde, a la Jessica Simpson. I have a few questions: -how often will I need to get my roots touched up? Right now I go every 8 weeks, and I am assuming that I will need to go more frequently if I go this light. -how is this platinum blonde color achieved? Through highlights, or over all color process?? -what are some great products to nourish this color, as I am sure it is drying to the hair. Thanks!!