Is your tub a drop-in or freestanding? I think the type of tub will help determine the answer. Just my opinion, but I would definitely want white if it's freestanding, because the tub color would "touch" the marble- with an insert, you would have room to mediate the color of the tub with the color of the marble as in the picture above. Notice that the walls are a complimentary shade, the trim of the arch and at the tub base is a lighter complimentary color, and then the marble is a blend of colors.