Lighter-colored shingles reflect more light and stay cooler in sunlight. And lighter-colored roof shingles help keep attic temperatures—and your air conditioning bill—down. But when it comes to comparing the life spans of dark vs. light, all bets are off. One major shingle manufacturer I spoke with said its tests showed no difference. Its position is that a properly ventilated attic provides enough cooling to offset the increased heat retention of dark shingles.
But some studies dispute that. They claim that since heat always increases molecular activity, and since dark shingles always run hotter, the heat factor alone dictates a shorter life for dark shingles. Yet another study suggests that the sun's UV rays play a much bigger role in shingle degradation than heat.
Just about all the experts agree on the importance of proper attic ventilation for longer shingle life. So my advice is to make sure you have more than enough roof and soffit vents and pick whatever color you like. Unless you want to save money on cooling—then you should choose a lighter color.