Original photo (I took a picture of my first car- it's like first love :0)):

Here is a result (you can choose any color you want):

Press D on your keyboard, so we could get default foreground and background colors.

This time we gonna use very powerful tool for selection- Quick Mask. You can simply press on Q on your keyboard or choose Quick Mask button:

Double click on Quick Mask button to get to tool's options. Choose Selected Areas, so our selected areas will be in pink.

Now choose Brush tool, set it's size to 5-10 pixels and choose all the areas that you want to repaint.

If you have selected too much(i got too much of a headlight)- don't worry, simply choose Eraser tool, and erase unwanted areas.

Make sure that you foreground and background colors are default black and white.

To select some small areas don't hesitate to use Zoom tool:

Finally all areas that we want to repaint are in pink.

Press Q on your keyboard, and you'll see such selection.

If you have some spots, press Q again and select them with Brush tool.

Press Ctrl+J, to duplicate layer via copy, and it's time to repaint our car!

Press Ctrl+D to deselect our selection. Image-Adjustments-Hue/Saturation.

In Hue/Saturation window click on Colorize, and choose any color you want.

I took yellow one:

Here you go! Got a different car!