Many cultures other than the Greeks and Romans practiced this technique as well. Not all stone should be painted or stained. For instance, one would certainly not paint over a fine Egyptian black marble or a beautiful African serpentine. However, when working with a very white statuary marble of perhaps a limestone, fine detail in a composition could get lost in the medium without shadowing and coloration techniques.
Often this technique was applied to reliefs installed into the gables of important buildings seen from a distance, where the sun might wash out detail. But, sculpture in the round was also frequently treated in this manner. The contemporary and abstract art today owes its appearance only to the artisan who created it. In 400 AD, art was truly about imitating life in all its color.
Steve Lynch, Stone sculptor