Christ,
I'm with you, in general. Like most things, there is really is no one "right" or "complete" answer.
For the OP, who was planning to repaint anyway, or for anyone that has the opportunity to choose the color of their vehicle (e.g. new vehicle buyer), evidence provided in this thread seems to indicate that a lighter color can help reduce the rate of heat build-up within the car. True, it may be negligible in some cases, especially if the windows are large and the interior is a dark color.
Certainly would not advise anyone running out and rattle-canning their new car white if they currently have a dark exterior color.
I would expect a light colored interior will help a little as well. And tinted windows would help even more (or instead of).
In the end, though, a car sitting out in direct sun for several hours will be friggin hot no matter what.
Best bet, as you said, is to park in shade or indoors, if that's an option. Maybe something like those 'bikini' car covers that just go over the passenger area with UV protection...