I discovered an awesome three colour combo while sketching in Greece. Cerulean blue + permanent magenta + yellow ochre (all Windsor & Newton brand). It creates some lovely shifting stone-like hues as demonstrated here in a quick sketch of the Lion Gate at Mycenae (scale provided by the little figure of a tour guide sitting on the left). The heads of the Lions are missing and were probably separate pieces made of wood, ivory or gold.
Behind the Lion Gate are the series of small stone walls that once formed the ancient settlement here and down the road is a gigantic honeycomb tomb. This is said to be of Agamemnon, king of Mycenae and star player in the famous Helen of Troy incident. After all his wars and triumphs the story goes that when he returned to Mycenae after the Trojan war his wife had taken a new lover. She killed Agamemnon by pushing him down the stairs.