I have a white car, and it's a little difficult when working outside to see just when to stop. Working indoors makes it a lot easier, but if you have to stay outside, just keep looking at the pad and use some polarizing sunglasses if you can. Inside, put a light at an angle to where you're working. In truth, experience is the only way to get a feel for working on white - I'm still an amateur. Good luck. After a few passes, you'll get a feel for it.
