CIE 1931 (x,y) Chromaticity Diagram and Color Mixtures
This applet shows how to mix monochromatic lights on the CIE diagram.
The dashed line indicated the possible mixtures of the two primaries.
The dotted line shows the line between a white illuminant and the mixture. The
intersection with the spectral local is the dominant wavelength of the
mixture (not shown explicitly). The fractional distance ratio from the mixture
to this point is called its excitation purity. (See a reference for
details)