"Painting ballast and sand to match" Topic

My friend bought a bunch of very nice river and road sections years ago. He always intended to get more, but the owner passed away.
I am trying to match the pieces, adding curves, T-sections, crossrads, etc.

The original were made from masonite boards, with what looks like a mixture of glue and sand or ballast. It could also be spackle or putty.
Anyway, I got a good texture match by smearing Gorilla Glue and pouring a sand and model railroad ballast mixture on the expanding urethane.
Now, I want to match the paint job.
What is the best way to paint and stain a sand and glue, or a spackle terain?
I experimented with mixing Liquitex bottled burnt umber with alcohol to stain it, but it comes out too thin and light. Am I on the right track, but not so much dilution? I also want the final product to be a dark matte brown, that I can drybrush some vegetation on with green craftpaints.

Take it to Lowe's and have them match the color to one of their paints then purchase a sample can of the paint and use that on the new pieces.

abelp01 is spot on with that suggestion. A can of dead flat matte house paint is the ticket to good terrain.

I have silica sand and railroad ballast as well. I use plain cheap craft paint, burnt umber as you did, the big bottle stuff. Mix in a little water so it will run in the deep areas.
Dry brushed with lighter color such as burnt sienna, then a second dry brush with a medium beige.

Spray paint it all black and redo all of them with the color set of your choice.

I wouldn't think you would want to start with stains, as they are too influenced by the color of the underlying material.

As a first step, I agree with adelp01. Then:
if the color of the banks are not close enough, then use a wash on everything of a darker color. The wash will act as a unifyer of the slightly different paint colors. Try being splotchy, large areas of uniform color are more easily picked up as different. For the water, add splotches of blue to break up any broad areas of color.

John whatever you do can you post some pics of the process and when done the final results.