This is fiddley but it sure looks nice. If you do this, use a dark ballast or ash to fill in between the rails. In some places, have no ballast at all as if the ash has sunk down completely.
Back in the olden days, railroads used to use that a lot on their ROW too, especially if they were poor, instead of the beautiful pristine looking granite and limestone we use today and definitely in yards and engine facilities if the ballast was used for the mainlines. I learned about this from the former VP of Boston and Maine. When he saw a route being made by Steamboateng for the Hoosac Tunnel, he remarked that the track layout was perfect but the ROW was too clean. ;-)
One of the issues I have with Trainz is blending rusty track and dirty ballast with a well-maintained ROW.