A standard white light is formally defined at W where . The monochromatic or the cent percent saturated colors form the outer border of this region while the colors in the interior of the horse-shoe are desaturated colors. The straight line in the bottom represents the various shades of purple. This diagram is very useful since this factors out the luminance and shows only the chrominance. So it doesnot show all the colors.
P be a color formed by .
The straight line joining white and P , meets the visual spectrum at C . Hence P is a desaturated form of the pure monochromatic color C . The wavelength of C is called the dominant wavelength of P . However, all colors do not have a dominant wavelength. These colors are called non-spectral .