This article explores the consequences of the Wyszecki hypothesis, that every color stimulus (radiometric function) comprises two parts, a fundamental and a residual. (Wyszecki's terms were fundamental color stimulus and metameric black. ) The fundamental alone is processed by the visual system and evokes the color sensation. The residual is not processed and is without effect on color sensations. The article develops relationships between color-matching functions, fundamentals, and orthonormal color functions.