If you've sprinkled sifted soil onto wet latex or glued it down, after dried try dabbing it with grassy green or yellower weed green. The effect is quite good. The size of the soil grains is about all you need in HO or smaller scales to represent blades of grass. It's not A1 perfect but sure seems to do the trick. After all, most times we are a scale 40 to 80 feet away from tracks viewing the RR. Our noses are not generally right next to the train ( though I do do that sometimes, put my chin right on ply for that really close view thing ).
Meant to say above; once you get a plausible green, not real bright like a well kept lawn but kind of dry or bleached, it's a decent effect that you start seeing after a while. Also soil not sifted finely so that larger clumps are here and there, when green, clumps looks kind of like weeds. I mix a little light blue into the green which makes it a bit mossy looking which looks good on hills and Mtn. crevices. I buy an inexpensive acrylic named 'Americana' at an art supply that comes in a squeezable bottle with a hinged cap for $2.00 each.
