Photoshop Elements 3 Tutorial
Start by extracting the object you want to change the color of. Any object will do, but shiny objects with high contrast are the best to work with since they already contain the shadows, mid-tones and highlights you need.
You may need to also convert your object to black and white using 'Image | Mode | Greyscale'.
Once that's done, create a new layer and fill it with color using the paint bucket tool. Hold down the alt key and click on the line between the two layers on the layers palette to wrap the color around the shape of the car and automatically remove it from all other areas.
Reduce the opacity of the color layer to about 65% and select the 'soft light' blend mode from the drop down on the layers palette. Use the eraser tool to erase color from parts that are not colored, that would be everything except the body.
Make sure you also erase the black areas to remove the color from them as well. You can create a colored background for your object and place it on the bottom (background) layer.
Experiment with the gradient tool to create soft background spot lighting that compliments the color of your object.
If you substitute a graphic for the color layer, you can even create the illusion of a custom paint job. Experimenting with different photos instead of the solid color will amaze you at the different effects you can achieve. Try to take your compositions a step further with different effects such as background lighting and reflections.
Play around with all the settings to get the desired effect you want on your composition. Try to recolor food or other unusual objects. These are powerful tools once you get a grasp on using them. Most of all, have fun!