Looking at your test tgd there is a Fractal Breakup shader connected to the Sand Surface shader but it has NO colour checked.
There is another Fractal Breakup shader connected to the Fake Stone Connecting layer as a Blender but it has http://www.arch.pw.edu.pl/?personal-essays Personal Essays no colour checked
Removing these helps, but by my testing I believe the real "culprits" are the Altitude constraint used in the Sand Surface shader
and the Slope constraint used in the Fake Stones Connecting layer.
Both of those two different constraints in different surface layers are attempting to be applied to the structure of the fake stones and colour.
The colour on the sides of the individual stones tries to stop at the slope angle you picked, instead of wrapping around the stone.
The Altitude constraint appears to actually try to stunt individual stones.
Here are a couple of renders with Base Colours set to red and blue. One with altitude constraints and one without. Some individual stones
get bigger as they were right near the altitude limit you set. Had to move the camera back and up so as not to be inside a now less restricted stone.
You can see how the Base Colours bleed in.