If you have a picture such as the first attachment, then if you go to image > adjustments > hue/saturation, then you click the edit: dropdown arrow (upperleft of box) and select the color your car is, then adjust the hue until you have your car the color you want. simple right? theres just a few problems though:
1.cars have to be a simple color that is included in the dropdown menu
2.the color of the car cannot also be in the background
3.when you make some adjustments to the hue the car becomes not a solid color thoughout
i made the car in attachment 2 in a matter or 5 seconds