Tom, Most of the gray painted area will be ballast. I'm going with a theme here that the right side to include the roundhouse was an existing railroad from way back (hence the abandoned coal tower and water tower that is being cut apart). That area will get a darker ballast. The left side with most of the newer style aluminum buildings will be a lighter ballast because they were built a lot later. There will be a lot of weeds and grassy areas everywhere. I need to go paint my roads back in, then a lot more will be clearer.