One of the vehicle testing engineers I talked to here in Arizona told me the vehicle color does not affect the interior temperature as long as the vehicle is moving at 25 mph or more. Given that on dirt roads you are frequently traveling slower than that, color is important.
I found that roofing paint works best, way better than white body paint. It doesn't look as good, but it is way cooler. I found mine at the hardware store - it was advertised as being good for the roofs of mobile homes, RVs, metal outbuildings, etc. I painted the top of my Series Land Rover (one without the tropical roof), and the surface temperature of it was cool. We had a white car at the time, and the roof of the white car would still make you hand uncomfortable on a hot day if you left your hand on for too long. The roof of my series truck was almost cool to the touch. What happens is, normal white paint absorbs a lot in the infrared wavelengths, while roofing paint is highly reflective.
You can't do too much with your windshield, but good tinting on your other windows makes a huge difference. There is no AC in my Land Rover, and I live in Tucson, and I have gotten the Land Rover to the point where the interior is rarely more than 5 degrees warmer than ambient. Which is still awfully uncomfortable when it is 108 out.
