I live near to one of the convenient routes to several police training facilities in my area and can usually count on seeing several cruisers on any given day. The Black and White scheme here in Maine seems limited to local departments. It is usually black on the hood, trunk and related fenders with a white cabin area, although I have seen a few in the reverse scheme.
As to the other colors, the various county sheriff departments run solid colors, white being most prominent for some odd reason. The state Police have a solid light to medium blue color, however the pick-up trucks used by the Commercial Vehicle Enforcement troop were a medium to dark blue. The Dept. of Inland Fisheries and Wildlife (game wardens) as well as the state Forrest Service use dark green pick-ups. Unmarked vehicles seem to be any solid color.
In terms of the make and model, Ford Crown Victoria and Chevrolet Impalas seem to dominate the cars. However when it comes to the pick-up trucks Dodge was the preference for about the last decade with Fords starting to replace them in the past couple years.
I hope this helps, my other suggestion is to look at news clips from the area you want to model as they are probably one of the quickest ways to see a good range of cars from different departments.
