No idea what features Elements has so if you can't find what I'm talking about ... apologies. Quick and dirty? Take your original image and desaturate, this would normally be under mode> adjustments> desaturate. Make a new layer above your original, pen tool the area you want to be your new color, fill with said color using paint bucket or whatever. To do this right click after you've outlined your car with the pen tool (pen tool should be set to "paths"), choose "make selection". Set blending mode to "Overlay" ... done. Blending mode should be on your layer palette. Don't think the pen tool is an advanced feature, you don't even really have to pull curves if quick and dirty is what you're looking for. It's not pretty but it's a quick way to try out several colors without coloring things like chrome or whatever, or put in stripes. You can try it, save it, reselect that layer, use another color, over and over in seconds. If you find something you like you can use the same method to make a nicer image later.
Quicker still is what Ben talked about. Mode> Adjustments> Hue/Saturation. Just move the sliders and watch with amazement. Anything with color will be affected though.
Ben talked about sampling a color from another image. To add to that, if Elements has it, use the "median" filter under noise I think. This just sort of blobs the image together and simplifies and solidifies the colors so you can eye dropper a dark, medium or light value of your color. Most images, especially poor quality, will have pixels filled with colors that might surprise you and median gets rid of that and gives your more pure color to choose from. There really is no such thing as an "automotive" color. Your image will more likely than not, be RGB, of hit or miss quality and it's up hill from there. You just do the best you can, especially if you're new to this. Don't be shocked if altering an image doesn't produce exactly what you want in color.
And in case you haven't read enough, google is your friend
http://www.graphic-design.com/Photos...ace_color.html this is a tutorial for Elements. It's slightly more advanced but will give you step by step ... nothing you can't do. Upon further examination, the second part of it is dead simple.