It's one way of conveying information the brain can interpret in a flexible way.
But the brain is also good at depth perception. Let's combine these :
For example in the app I released yesterday StlToRelief : https://news.ycombinator.com/item?id=22319140
I use a color gradient to increase the perception of depth. It makes a thin bas-relief standout.
With color-mixing 3d-printing this is an effect we can now exploit.
There is a closely related phenomena that we have when doing war paints for camouflage. Area (i.e. peaks like the nose) that would naturally catch the light appear brighter so you have to paint them dark while hollow area that naturally appear dark must be painted white. The resulting painting make a face look flat which stand out less.