Four courtyard green brick gray tile, the color is not colorful is the reason? The gods help

"When the roof of a courtyard house is basically finished, it will be built with a gray backing made of a mixture of grass and clay, and on top of that the tiles will be laid. In this way, the gray backing is laid in a thick layer, which has the function of preventing rain and keeping the heat in." So the answer to this question is to prevent rain and play the role of heat preservation. Because Beijing is located in the north, summer is hot and rainy, winter is cold and less rainy, in order to cope with the change of climate, the courtyard adopts green bricks and gray tiles to prevent rain and keep warm. Because of the materials used so colorful.