What is a green house made of?

The saying is "If a blue house is made of blue bricks and a red house is made of red bricks what is a green house made of?" Well it is made out of glass. A lot of people think it would be made out of green bricks because if a blue house is made of BLUE BRICKS and a red house is made of GREEN BRICKS it only makes since that it would be green bricks. But its not. The answer is "Its made of glass!"