Yard ballast would be very small ballast 1/4 to 1/2 inch diameter because people have to walk on it. "Main line" ballast would be much larger, in the 2-3" diameter range.
Whatever the finest ballast you can get, use that for the yards. Modern era could be the same color as the main, but much, much smaller particles.
Dave H. Painted side goes up. My website : wnbranch.com
I am building an N scale version of the Virginian layout, slightly modified, after a long time away from hobby. I am modeling Chessie System mid-1970s. The MR version of the layout used cinders in the yard and mine run track and after my re-education in the hobby realized the use of cinders as ballast was probably steam era related. I am using light gray mainline ballast based on Chessie mainline photos but can't find any good yard shots aside from oil soaked ballast (noted for engine track). I have all the yard track set flat, no raised roadbed, used Woodlands foam sheet. Any thoughts on yard ballast color. Thanks.