Gustave Caillebotte (1848–1894) was part of the French Impressionist art movement, the first school of art to break away from classical painting. Impressionism focuses on the light and colors of a particular moment in time. Because artists wanted to capture a brief moment and didn't have cameras yet, they needed to paint quickly. So they used quick, flat strokes without precise detail.
They also used colors in new ways. The best example is that shadows aren't just the object's color with gray or brown mixed in. Instead, the painters added strokes of the complementary color of the object (e.g., strokes of red in the shadow of something green). This makes the shadows come alive.