Color Field
Clyfford Still, Barnett Newman, Adolph Gottlieb, and the serenely shimmering blocks of color in Mark Rothko's work (which is not what would usually be called expressionist and which Rothko denied was abstract), are classified as abstract expressionists, albeit from what Clement Greenberg termed the Color Field direction of abstract expressionism. Both Hans Hofmann and Robert Motherwell (gallery) can be comfortably described as practitioners of action painting and Color Field painting.