You obviously never owned a white car. As all colors go, white shows dirt less than most (best are light grey, silver - the darker the color the quicker it shows dirt). Black on the other hand shows dirt and fingerprints within 24 hours of washing, no matter where you drive and park. White just gradually gets dimmer as dirt covers it, but it's much less noticeable unless you clean a part of it (or write on it with your finger). There is an exception for white though, if you live somewhere with red clay for example, the red dirt does show up on white. Most places however don't have bright red clay, so it's not a common issue.