 Originally the police cars were going to use the NYPD blue and white  paint scheme. A few screenshots of them can be seen in the  map/poster that comes with the game (the best one is right under the  word "Liberty" in the title "Welcome To Liberty City"). It is  believed that the police cars were changed to the standard black and  white paint scheme to make them not look like the NYPD cars because  of the terrorist attacks on the USA of 11 September 2001.