For this desert scene I used different shades of tan for the sand on the sun side. The more directly the sun hit the sand in the picture the more redder it got so i used differen gradients on the same selection to achieve the right tone that i wanted. The parts where the shadows hit the sand dune i used different shades of blue to an almost black color. You can see in the picture how the shodows blend in with the concavity of the sand dunes. The sand in the foreground gives a good reference point as to how far away and how massive the sand dune in the background is.