To do this tutorial you must have a great understanding of the pen tool in ADOBE PHOTOSHOP, i will not go throu each individual stage and walk you throu every little thing i do, you will be left to your own devices, but will help you the best i can.

Copy the "base color" layer and put it under the "highlight" layer but above "shadows" layer. Color the copy of "base color" the color that you want the car to be. By having the color on a separate layer, you can change it later and it won't affect the shading at all. also play with the opacity of "highlight", "base color" & "shadows" until you get a look you like this.