Light Vs. Dark
Light and dark shingles are set apart by their reflective properties. Light shingles, because they reflect more of the incoming sunlight, keep your attic and thus your house a bit cooler than darker shingles. Dark shingles, on the other hand, can warm your house in a cold environment.
Where Light Shingles Work
Light-colored shingles are superior in places where increased heat is not an advantage. This includes any place with a warm climate where most of the year is hot. Cooling costs can be decreased by using a lighter colored shingle that reflects some of the sun's intense heat away from your home.
Where Dark Shingles Work
Dark shingles are superior anywhere it is an advantage to have an extra source of heat. If you spend most of the year with your heaters on, then darker shingles will give your house an extra source of natural warmth.