I have plenty of airbrush equipment, but I've found my best rail and track colors, which appear to be very similar to what you're attempting to do Ed
@Ed Kapuscinski to be accomplished using rattle-cans of Krylon or Rustoleum paint.
The colors I use are Ultra-Flat Camo Black for the rails, and Ultra-Flat Camo Brown for the ties.
These two colors act as base colors for the rails and ties....how they're applied making the difference in how they appear after application.
First step is to spray the track, ties and all, with the Camo Black, the object being to spray mainly from various angles to get the sides of the rails and the sides of the ties. Of course, the tops of the ties are going to be covered too in this step, but getting the rail sides is the most important.
I make sure I'm spraying light coats always. I don't want thick paint to obscure my ME C55's track detailing, and I want it to dry quickly.
Next, after waiting about ten or fifteen minutes for the paint to "dry" (not "cure") I remove the first coat from the tops of the rails using an old flexible Brite Boy track cleaner. This process goes pretty quickly.
Then, I spray a very light spray of Ultra Flat Camo Brown from directly above the track...like perpendicular to the tops of the rails...so that there's a very light coat of Camo Brown that covers the tops of the ties, with only overspray lightly dusting the sides of the rails and the sides of the ties.
Again, I wait ten or fifteen minutes, then remove the uncured paint from the tops of the rails.
This gives a very nice grayish/brown color to the sides of the rails, and a good medium brown base coat for the ties.
Next, using prototype photos, I brush paint individual ties...with various shades of tan, brown, and grey...varying the colors randomly...not brush painting every tie, but enough to get a fairly prototype look using my color prototype colors as a reference.
Depending on the track, I'll apply either a dark wash to the ties, or dry brush them with a lighter color....
Then, I ballast my track.
After ballasting, I break out my Paasche VL and apply light dustings down the center of the ties, coloring both ties and ballast with either grimy colors or a reddish color (which represents UP weed killer used on UP mainlines up Weber Canyon).
Finally, I add color details such as little piles of sand on up-grade trackage, brake dust on down-grade trackage and grease where there are flange oilers.
UP is always tearing out old ties, replacing them and re-ballasting, so there are sections where the two mainline tracks in a section don't match, one being newly ballasted with new ties inserted, as opposed to the older, more weathered trackage on the adjacent mainline.
This works well for me, and from my photos, it appears very similar to what you're trying to accomplish color wise.
Photo (1) - Painted, weathered and ballasted dual mainline trackage in Wilhemina Pass using the rattle-can Camo Color track painting method:Photo (2) - Closer view of track painted using rattle-can Camo colors:I've done this for years, the only drawback being that the non-acrylic Camo paint will eat Styrofoam if applied thickly...but I prefer the non-acrylic version, so I keep my coats light.
It's also important to apply from directly overhead and in very light coats so the sides of the rails don't get covered completely with Camo Brown.
Cheerio!
Bob Gilmore