Many police department have implemented black cars to be less obvious. Many have the word "police" in some kind of paint that can only be seen when the light hits it just right.
Even flashing light bars are now hidden or minimized so that one does not realize is it a police car. Colors, letter, and shapes selected to not be so obvious - until they light up with many flashing colors (red, orange, white, and blue).
Some Jersey State cops suspended or fired (never knew which) for routinely drag racing on the Garden State Parkway. In cars that were not entirely obvious.