Let's paint your car, without the cost and pain of dealing with your local Maaco.
I started with this photo of my Ferrari. Ok, so it's not my Ferrari. I actually got it from maximum-cars.com.
The first and hardest part is going to be creating a mask for all the painted areas of the car. Now, don't get mad, but I'm not going to tell you a super-easy way to mask, or select the painted areas, simply because there really isn't one. I will link you to a tutorial on masking though.
Here's a mask of my selection:
What you're going to want to do is start with all the colored areas you want changed selected. Then create a new Solid Color Adjustment Layer and pick the color you want the car changed to.
This is also a good time to find and correct the areas you might have missed.
Now, we have a few different options for changing the color, depending on what color you started with, and what color you want. There's basically three or four Layer Modes we're going to experiment with to see which one produces the best results for our color.
The first Layer Mode is we'll try is Color Burn.
Not bad. Let's try another one. Let's try Overlay.
Kind of cool, but not the color I was looking for. Now, let's try Vivid Light.
Now that's a little intense. Not what I was looking for either. For the last one, let's try Color.
Well, that's pretty, but still wrong.
It seems like, for this project, the easiest change would be to use the Color Burn Mode.
Now, what if I want to make the car white? Let's take the painter's approach. Change the color on your Adjustment Layer to Black, then set the color mode to Color. This will desaturate the image, almost like a painter uses primer.
In this specific case, my car ends up looking pretty white. But, yours might not look the same and I can make it whiter. So I'll duplicate the Adjustment Layer Ctrl-J, set the color to white, and change the Mode to Soft Light.
And now I own a beautiful, rare, white Ferrari... err... at least a picture of one.
