Probably the best and easier way would be to take a photo of the vehicle and use this in a Photoshop type programme where it is an easy task to alter colours at will, so as you can choose the colour you'd like your car to be finally painted.
If you yourself do not have such a programme then others might or you could visit a site such a SERIF and choose a free sample version of Photoplus to help in your quest.
Paint is expensive, and a GOOD paint job requires several coats of paint. The cost can run into the THOUSANDS of dollars. Unless you have unlimited funds for this kind of application, I suggest you decide on the final color BEFORE you start painting.
If you have the money yes. Bear in mind a good colour change paint job is £££thousands. Anyone advertising it cheap will be sh1t.