One trick that worked out quite nicely was to have Sherwin Williams mix up a sample can matching GW Calthan Brown. The paint is out of production from GW, but that is not the problem. It is a nice dirt brown, but every manufacturer makes colors that work well as dirt. The problem is that basing can use a lot of paint, especially when you’re painting over glued sand. It is much cheaper to use a matched paint (or really just whatever dirt-brown catches your fancy) from Sherwin Williams, Lowe’s, etc. The paint is at least as durable, and you can get a container the size pictured for about the same cost as 2 pots of GW paint.
Bases coated in one coat of matched GW Calthan Brown: