There should be a lot of orange coloured bricks. Not all the walls would be covered. However, look to this not for the sake of photo realism, but for the sake of grasping the layout and size of this marvel of an ancient city.

Looking at the scope of their architecture projects (the Circus Maximus dwarfs everythig around it) I can't help but be amazed what people could build 1700 years ago. Actually there is a Roman bridge in Spain that is stil in service today...