Arranging spectral colors in a circle to predict admixture of light stems from work by Sir Isaac Newton. Newton's calculation of the resulting color involves three steps: First, mark on the color circle the constituent colors according to their relative weight. Second, find the barycenter of these differently weighted colors. Third, interpret the radial distance (from the center of the circle to the barycenter) as the saturation of the color, and the azimuthal position on the circle as the hue of the color. Thus, Newton's color circle is a predecessor of the modern, horseshoe-shaped CIE color diagram.