An artist, when he paints a tonal picture, has in mind the relative dark and light of colors, and their relative coolness and warmth. Let me explain. First the relative coolness or warmth of colors. The artist regards blue as the coolest hue. As a matter of fact violet reflects even less light than blue; still, for his practical purposes, an artist says that the cool hue is blue, and he associates with it violet and green. On the other hand, yellow, he treats as warm, and associates with it red and orange.