Selecting large areas of the same colour is one of those few occasions where the Magic Wand tool is actually useful, so weâ€™ll use it as a starting point here. With a tolerance setting of 20 it should be able to pick out the car bodywork without too much trouble.
With the Magic Wand, itâ€™s best to add a bit at a time. Click on an area thatâ€™s a mid-tone for the total area you want to select, and youâ€™ll find that the wand tool will select an area around it. The size of the selection will depend on the tolerance setting. By holding down the Shift key and carefully clicking on areas around your starting selection, you can add more areas. If the wand selects part of the background, use Ctrl-Z to undo that step, and try again more carefully, possibly adjusting the tolerance downwards if it keeps happening.
When youâ€™ve reached the limit of what you can usefully select using the Magic Wand tool, you can finish your selection using the Polygonal Lasso tool. By setting the Feather to zero you can produce a sharp-edges selection.
Again hold down the Shift key to add more areas to your selection. If you need to remove any areas from the selection, such as door handles or the number plate, you can subtract by holding down the Alt key and going around them with the Lasso.
When youâ€™ve selected all the bits you want to repaint, you can save the selection for later use, so you don't have to do all that work again if you change your mind.