As below poster said bright sunlight is required. Some paints are really hard to match, therefore, when you repaint the door you would also father the paint ont

As below poster said bright sunlight is required. Some paints are really hard to match, therefore, when you repaint the door you would also father the paint onto fender and quarter panel. Additionally, there is something called "orange peel". Most cars have it, it is extremely difficult to match the original orange peel pattern. Often the new clear coat is wet sanded and then buffed which can completely remove the orange peel. It is quite easy to spot these things by a trained eye, and generally if a one cannot spot repainted panels it is most likely a job well done.