Yes, you absolutely can buy multiple Username Color Changes and switch between them. You'd only have to purchase a new one if you want to use a color you've not used before, i.e. if you've already purchased and configured 3 items, you can't reconfigure them to a new color and would have to purchase another item, if that makes sense. You're stuck with the color you entered once you configure and save, but from then on, that color change remains in your inventory and is available for use. You just have to click the "active" box on whichever one you wish to use at that time.