I once had a topper painted to match my pick up truck. The shop laid this "camera" type piece of equipment on the hood then again on the side panel of my truck. It completely blocked out the outside light and used its own internal light source to get a reading of the actual paint color. So even if your cars paint has faded some from its original color from the factory...the paint they painted my topper with matched the paint on my truck. I thought it was a pretty clever way of doing it.