The Colorful-Uncolorful Contrast

Two colors with different luminosity show a colorful-uncolorful contrast. All shining and intense colors have a great luminosity; all subdued, dull and gray colors have a low luminosity. Example: misty rose and green. Misty rose has a low luminosity, and green has a great luminosity.
It is best to rely on your instinct when trying to determine whether a color is colorful or not. Even Roman Liedl writes: "One can hardly give a formula for the determination of a color's luminosity. Personal sensation (which even differs with one and the same person) is always a very decisive factor".
So you could say that colors quickly lose their luminosity when mixed with gray (as is the case with misty rose, which is a mixture of magenta and gray).
 
As mentioned before, black, white and gray areas do not influence angular harmonies. But they can be used as partner for a colorful-uncolorful contrast. Example: If a web site contains a 2-color harmony of deep green and deep magenta, the missing colorful-uncolorful contrast can be produced with both black and white. Black or white then represent the uncolorful color, and black is especially suitable for this purpose.