Color theory primary colors work at all is that the imperfect pigments being used have sloped absorption curves, and thus change color with concentration. A pigment that is pure red at high concentrations can behave more like magenta at low concentrations. This allows it to make purples that would otherwise be impossible. Likewise, a blue that is ultramarine at high concentrations appears cyan at low concentrations, allowing it to be used to mix green. Chromium red pigments can appear orange, and then yellow, as the concentration is reduced. It is even possible to mix very low concentrations of the blue mentioned and
Orange (colour) Winslow Homer brightened his palette with vivid oranges. In France painters took orange in an entirely different direction. In 1872 Claude Monet painted "Impression, Sunrise", a tiny orange sun and some orange light reflected on the clouds and water in the centre of a hazy blue landscape. This painting gave its name to the impressionist movement. Orange became an important colour for all the impressionist painters. They all had studied the recent books on colour theory, and they know that orange placed next to azure blue made both colours much brighter. Auguste Renoir painted boats with stripes of chrome orange