AbstractThe color appearance of the hue cycle in equal radiance is described in hue, saturation, and brightness/lightness. The latter does not resemble CIE luminance Y (peaking at 555 nm green), but peaks near 570 nm yellow with minor peaks near 490 nm cyan and 530 c magenta. Saturation per watt peaks near 450, 530, 610 nm (blue, green, red). Newton's choice of seven spectrum colors, and particularly his two bluish colors, is explained as major colors rather than merely different hues.