Ron, I think you are pretty close to achieving the grimy cinder ballast look. I have been trying to get the same effect in my engine service facility... the first 2 tries were epic failures.... 3 rd time is definitely getting better, I think I like yours better...
I ended up putting down low loft batting , between the tracks over a layer of cork to bring up the ground level Then i painted the batting with a heavy coat of dark brown latex flat paint, then spreading ballast that I had spray painted dark gray and black, as well as a lot of dark dirt, plus scenic cinders, and a little black beauty sand blasting media... ended up sprinkling a hint of "burnt grass" foliage foam (very fine)...
As I keep moving along, I think I will only ballast lightly between the rails, and use the dirt and cinders right up to and in between the ties.... I also, tinted my white glue mixture with india ink to try and darken the area further.
Not sure if any of those ideas help.....