I highlighted all the areas on the riders. The main highlight color I used on all colors except for the browns, metals and whites was Vallejo 70.858 Ice Yellow. This toned down the garish colors all over the models, and brought them slightly closer together.
I then hid the integral bases of the horses with filler, into which I pressed some larger stones.
Once the filler was dry, I brushed on PVA and sprinkled the bases with finer sand.
Once the PVA was dry, I secured the sand with scenic glue (acrylic medium/alcohol mix).