To all that are familiar with Photoshop. Here's something I helped a forum member with on another website. It is laying graphics down the easy way utilizing the pen tool/Bezier curve tool.
Changing of paint or graphic schemes.
1. Make a copy of the original color (body outline) using pen/Bezier tool
2. Desaturate color - Image/adjust/Desaturate
3. Make a copy an fill with Color of choice (make sure this copy is
above the previous desaturated color).
4. Go to layers palette, (the new color layer) go to overlay or screen
(top left pull down tab) you can adjust the transparency to desired effect
and there you go.
Give it a try.
Here is a sample pic: The car had no graphic prior to me working on it.