But so far we have been thinking only of one team, working out its scheme of attack and defense in practice play. There is a more complicated play, namely, when the team is pitted against a rival team. So in color. An artist will introduce rivalry, or competition into his color scheme; namely, two crack notes of color that, seen by themselves, would produce a disagreeable sensation. Why does he do so? Because he knows the value of contrast and discord; just as you know it is more fun to watch a game of football between two well-matched rival teams than the merely practice play of one of them. For now the artist is pitting one set of colors against another set; the crack players on both sides and their backers-up--the colors of different but closely related hue; and the game between them is fast and furious--an interplay of likes and unlikes, of repetitions and of contrasts. The excitement of the game results from the even balance of the two rival sets of colors, swaying backward and forward over the gridiron--I mean the canvas--massing here and there, then scattering in a burst of animation--the two teams so evenly matched that their rivalry only makes the give and take of the game more brilliantly harmonious.