André Derain, 1905. Co-founder of Fauvism — pure colour landscape. National Gallery of Art, Washington.
From Wikipedia
Mountains at Collioure is a 1905 painting by French painter André Derain. It was made while he was working with Henri Matisse at the fishing port of Collioure, in France. It has been in the National Gallery of Art in Washington, D.C. since John Hay Whitney, the previous owner, died in 1982. The work features long strokes of colours such as bright green, blue, mauve and pink. The entire scene is under a jade and turquoise sky.