Here I will show you how to repaint a car, but once you master the technique then you will be able to apply it to other objects or graphics with ease.

1. Open the picture that you want to apply this technique to.

Select the pen tool

2. With the pen tool, trace the car. Don't worry about any details. Get something like this:

Now that you have traced the car, create a new path, name it windows, and trace all windows of the car. Do the same thing for the mirror, lights and etc. You will end up with something similar to this:

3. First Ctrl + Click on the "Car" path.

Once the car is selected, Ctrl + Alt + Click on all other paths.

4a. Keep the selection, and create a new layer.

In the new layer, fill the selected area,with the color you want your car to be. (Select a stronger color than the one you want.)

Then, change the Blending Mode to color.

4b. If you aren't happy with the previous result, do everything except the 4a.

Then, go to Image -> Adjustments -> Color Balance or you can simply press Ctrl + B. And try to get the color you want.