Most of what we know about Greek art comes from pictures the ancient Greeks painted on pottery.
3 periods/styles of Greek vase painting are: 1) Geometric Period 2) Archaic period (black & red figures) and 3) classical period
During the Archaic period, Greek potters made claypots with mythological scenes on them. At the same time a new painting technique developed called black-figure. The Greek potters painted people in silhouette and painted the people all black.
Then somebody had the idea: instead of painting the people black, why not paint the background black and leave the people red? This is harder because you have to carefully paint all around the people in the picture, but it makes the people look much more real.