The three primary colors, from which all others are generally conceded to be derived, are' red, yellow, and blue. They cannot be produced by any combination of other colors. Some authorities insist on seven primary colors, and another theory derives all colors in the world from pure red, yel low, green, blue, and purple. It asserts that no matter how light or how dark, how bright or dull any color may be, it is derived from one of these five. The debatable question of color-standard, however, does not come Within the scope of this manual. J.