Thanks Frank and Fredrik.
In the top picture, I have painted the tire a dark gray and the wheel cover is a CDL color using gloss enamels (since there are decals to be applied). After decaling, I sealed the wheel with Future clear coat. Then comes a flat coat using Testors lacquer flat coat which makes a very flat color. Then I used a sponge to dab some dirt colored acrylic water based wash on the tire, working it around on the tread surface. Just when it looks like it needs a little more - STOP.
From the pictures I have seen, German tires are a lighter gray than British tires.