That would be better, but for most places, there isn't much solar energy coming in during the winter, so they aren't losing much by being white. Maybe for wint

That would be better, but for most places, there isn't much solar energy coming in during the winter, so they aren't losing much by being white. Maybe for winters the best would be to use fluid based collectors with coils inside the envelope of the building to skip the energy past the insulation. With a low sun angle you don't need much area of them to capture all the sun and in the summer they would provide shade to a portion of the white roof. Now, if only they were free.