I know at one time, the majority of all cars sold were at least some sort of red in color, so it only makes sense that more red cars will get citations. If they are using a laser, it is pointed at an individual car. If it is a typical radar unit, it sends out a wave and measures cars coming at the radar and gives a speed. It is up to the officer to determine which one is going the fastest. Most officers have been trained to just look at a moving vehicle and determine the speed at which it is going.
Unless you know that the area you are driving in is a speed trap, keep it at about 5-8mph over the limit and you shouldn't have much problem.