Sheesh, sorry, way to leave out a vital point, Princhester 
Ahem. The dark cars were hotter.
As to a range. Hmmm. I’m surmising as much as remembering, here, but I do recall thinking the difference was huge, and I suspect that means 2 digits or at least close to that. So maybe about 10 degrees celsius might be about right. Take this with a great degree of skepticism though.
Hey GuanoLad and MasterBlaster: thanks for the tip, I searched Wikipedia for the Mythbuster’s experiment, and found this from their third season:
“A fan wrote in and asked a follow up question: “Does the color of a car affect the way it heats up?”. The MythBusters used two identical cars, one black the other white and left them both out in the summer heat with thermometers in both. By mid-afternoon the black car had heated up to a temperature of 135°F while the white car topped off at 126°F, almost 10° cooler.”
Excellent! This is much less extreme than the graphs at Car Color Surface Temperature Data would suggest, probably because they were measuring temperature a little differently (just under the roof, as against some sort of average measure in the interior, I would guess).
Another thing to consider is what color you pick for the inside of the car. And the strength of the sun. I don’t live in a hot area, but I do live at altitude and I do get down to Denver enough that made me chose a tan interior over black.
In theory, yes. White paint is actually a decent radiator, even when it’s sitting in direct sunlight. It absorbs very little visible light, but emits infrared just fine. Just put a thermocouple between a black metal plate and a white plate, and you get electricity.
But it would be even more efficient if you put the radiator in the shade. And even then it won’t be as efficient as a photovoltaic cell (regular solar panel).
Some anecdotal evidence – last year I lived in Sonora, Mexico – the Sonoran Desert. It gets to 120 in the summer. It sucks. My company car was a black car with a black interior. Who the hell in their right mind bought this thing? None of the locals ran around in black cars. If I didn’t park in the shade or throw a towel over the steering wheel, I couldn’t grip the thing. The residual radiant heat from the interior was such that the air conditioner wouldn’t do a thing to make the cabin comfortable in the 25 minutes between work and my house. It sucked, and it sucked big. At the same time, I had a personal vehicle there – different make, but I’d bought it in Arizona, which is also in the Sonoran Desert. Grey exterior, grey interior, and perfectly tolerable after being parked in the sun all day.
On on the road again, and now my loaned car is black with a tan interior (happens to be the same car that I was in Sonora for in the first place). Ontario had a major heat wave last week, and despite being black on the outside, it was just as comfortable as my own personal car with a tan interior and a maroon exterior. (All the same, the company loaner has air conditioned seats! Man, I’ve got to think about replacing my aging personal car!)
What is it about cars that make them special? Don’t most dark things absorb more heat than most white things? Especially when other factors are the same?
In general, yes. But there are exceptions. For example, black clothing can keep you cooler than white clothing under certain conditions. Since a car is a fairly complex system, it’s perfectly reasonable to ask if a black car is really hotter, and if so, whether the difference is significant or not.