Depth: blue 54%, grey 13%, white 10%, …
Heller E. (1989)

Research into the orientation of Impressionist or Expressionist paintings shows that expressionism, with mainly portraits and still lives as the subject, has a majority of vertical paintings. While impressionism, with landscapes or outer views as an important subject, counts the most horizontal paintings. Verticality has deeper subjects than horizontal. “They sought around with the eye and not in the mysterious depths of the mind.” Gauguin, about the superficial representation of reality among the Impressionists.
(Alpaerts, 1980)