Intensity: The Third Dimension of Color
Intensity is the third dimension of color and refers to the strength, saturation, or purity of the color. In most cases, the color is at its greatest intensity as it comes from the tube.
To reduce the intensity of a color, white may be added to lighten it or black may be added to darken it. In both cases the purity of the color is decreased. Also notice that as the intensity is weakened, the value has changed. The intensity of a color can also be weakened by adding its complement. For example, blue can be grayed by adding orange.
Nature is full of such a variety of colors! If one is doing landscape paintings, it is very important to be able to control intensity, value, and hue, because changing one nearly always changes the other two as well.