This study seems to say painting them white will do so.
If you live in Florida and your AC energy bill is $2400 a year than that is $240 in energy savings or $20 a month.
Obviously that's not enough of an energy savings to actually make it worth repainting your home, but if you are going to repaint anyways, why not make it white?
Intuitively it sounds a little high. Any real world experience with this?