It looks like you have set this surface layer to be applied to all surfaces (flat) up to 30 degrees. The color you have set is gray which seems to be correct in your image.
A thing that helped me understand if I had conflicting surface layers - two surface layers where one overwrites the first; is to use the Test color checkbox and also the Enable checkbox.
Check one surface layer at a time to determine if that is what you want. To do this, disable (uncheck) the "Enable" checkboxes on all but one of your surface layers. With one surface layer enabled, use the test color to tweak how it lays on your terrain. Do this for each successive layer, until you get the desired result.
Hope this helps...
JR