There is a reason why during a tornado the clouds are green. The tornadoes pick up whatever vegetation is in their paths and that turns the clouds green. Since the tornadoes travel mostly over open land, this makes a lot of sense. But some day, I suppose, when all this land is settled, covered with buildings and houses, the clouds will change color. They will be gray with cement, lead, asbestos, or whatever is still legal to build with in the future. Or perhaps they will be clear, like the glass from the windows they pick up. They will be transparent.