since the theme of my army is sortof more cliff dwelling more incan lizardmen I decided all of my reptiles would be grey and stony. to problems I have come across. I did the skinks in fortress grey with codex back scales and the backscales got a wash of badab, it looks great. the saurus I did in codex., their boney head ridge thing is adeptus along with the spines that go down the middle. but for the back scales I have no clue what color I wanted it to be different to make the frill and spines stand out more. I had an idea though that I will first probably test on my kroxigors if people think it's a good idea. Moss, taking some of my flock I ordered painting watered down glue then flocking the back scales so they look like they move so little they started gathering moss. if that is a bad idea what would be a good color for the back scales that would make the spines stand out. I was still thinking green, maybe my gobline green a wash of thraka then dry brush goblin over it again. current back scales are just badab over codex then drybrushed codex again the shield is dheneb, then a sepia wash then dheneb again.
You could add a light drybrush of a lighter grey. If you look at the saurus warrior I painted in my army log post, you'll see I went from a very dark grey to a very light one to make the scales stand out a lot. You can find my army log link in my signature.