As value controls our perception of light and volume, so chroma control defines their quality. Chroma, or intensity of hue alleviates the stress of viewing a world of pure hue. We use control of chroma to make our humble abodes more livable. Try to imagine sleeping in a room decorated in day-glow green. Chroma works hand in hand with value to portray surface quality, dimension and depth. It slows down the natural vibrations of pure hues and aids in the digestion of the beauty of color.
Conjure up your color tree for a moment. Visualize the leaves on the hue branch called red. Now look at you color wheel. We have painted it a highly intense red; the red that is the last leaf at the tip of our red branch. I have explained previously that as the leave sprout closer and closer to the tree's trunk, they progressively become duller, grayer less like red on our color wheel. But ,how does that happen? Not with magic, I assure you. It occurs naturally in some colors and through manipulation with others.
To manipulate a highly intense red, we can add the color that lays directly across the color wheel, namely green. When combined together, they become a tertiary or gray. This is indeed another function of our color wheel, in that it enables us to quickly identify any hue's chromatic opposite i.e. blue/orange, yellow/violet, etc. To this end, there exists a perceptual phenomena called Successive Contrast. If one stares at an intense red for about thirty seconds then looks at a piece of white paper, the chromatic opposite will appear as an after-image.
Another method in manipulating chroma is to add black or white to the hue. This time we are also altering the value of the hue, although this may not become apparent until a combination of black + white is added to the hue. This method illustrates how value and chroma work hand in hand in color harmonies.
Two final alternatives in manipulating hue remain. They are achieved by mixing a hue living next door to our chosen hue (need to use your color wheel again) or a hue from the same color family that is naturally duller by adding a choice from a group of toners called the earth colors. The latter receive their descriptive name from the fact that the pigments come from soil.