Or at least, white is right if solar collectors aren't an option at the moment:

From "The New Republic" energy blog:

"Bust Out The White Paint!" by Bradford Plumer

Excerpt:

"just refitting the 30 billion or so square feet of commercial roof space in the United States would be the equivalent of taking roughly 75 million cars off the road for a year. And, as a bonus, buildings with white roofs tend to stay 30 percent cooler than their black-topped counterparts during the summer, which curtails energy use. Obviously this wouldn't stop global warming, but on the list of pain-free measures that would make a fair bit of inroads on the problem, this has to rank very high up there."

75 million cars?(!)