Personally I would like to see the car body itself a solar cell but would not appear as so, it can be painted with a certain paint to simulate colors or graphics, just the car sitting in a car lot, shopping mall lot, at work or at home it can charge into a local grid.
Painting over a solar cell is going to block the light used to power the solar cell.
The amount of energy captured would be negligible. In full sunlight the best available solar panels now, sized to cover a car, would only deliver a few hundred watts and even at 100% efficiency could not produce more than a couple of thousand watts, so it would take weeks to fully charge a car's batteries that way. Even parking all day in full sunlight would not add more than a couple of miles to the vehicle's range.