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) paint straight from the tube. Paul Cézanne did not use orange pigment, but created his own oranges with touches of yellow, red and ochre against a blue background. Toulouse-Lautrec often used oranges in the skirts of dancers and gowns of Parisiennes in the cafes and clubs he portrayed. For him it was the colour of festivity and amusement. The post-impressionists went even further with orange. Paul Gauguin used oranges as backgrounds, for clothing and skin colour, to fill his pictures with light and exoticism. But no other painter used orange so often and dramatically as Vincent van Gogh. who had