Long ago I had a gallon of latex paint mixed at Lowe’s to a beige color. When at your big box store take a look at the “Second’s” rack. Often half-price or more anything from gray to brown .. cheap enough to mix and will work as a base color.
Pigment
Once the paint had dried the next step was to sprinkle brown powdered Tempera. I simply dipped a brush into the pigment then with the brush over the project I tapped the ferrule of the brush against my hand.
Spritzed water
Tap water in a spray bottle is then spritzed over the Tempera powder washing the pigment into low areas and across the face of some of the ‘stone’. This can be done as needed – waiting for the surface to dry and adding pigment and then a spritz as needed.
Dry Pigment(s)
Notice how the pigment pretty much acts as a filter with nice coloring to our ‘rocks’.
AI Spritz
Next we want to add shadows. I used a AI (Alcohol, India Ink) mix spraying this on. Again, less is more. Spritz some on and let dry then if more is needed, repeat the process.
Zip Texture
This next step might not be needed but IMO layering of texture and color add to the finished product. Zip Texturing is where you use a mix of plaster and Tempera sifted over a moist surface. This gives the grainy look of earth.
Coloring finished (for now)
So. Here we are with the rock and dirt ready for additional steps. IMO .. not bad for such a series of simple steps.
Rocks, Gravel and Stuff
My favorite source for rock and gravel etc. is Paver Base. This can be found at your building supply store. It is used to level paver blocks. It is decomposed granite and you can’t beat the price. Lowes has it in bags for $3.49 for 0.5-cu ft. I use a variety of silves to get everything from very fine to very coarse material. One bag lasts for a long, long time.
Here I sprinkled fine stuff, then some medium and finally larger rocks on the diorama. I used white glue and water to set everything in place.