This code will give you a black police car.

It can also be used for Ambulance and Fire Engine.

First Thing You have to do is enter the code:
X, X, Down, R2, L2, O, R1, O, Square

This code is for the Japanese Theme

It turns all automobiles black and everyone rides a black FCR - 900

Once you have done this, find yourself a police car and steal it and put it in one of your garages at your safe houses, then re-enter the above code to de-activate the cheat.

When you take the police car out, it is still black but everything else is back to Normal.