This phenomenon was first noticed by French weavers. When they wove two colors such as green and red into tapestries they noticed that the colors from a distance became muted. They also noticed that other colors in close proximity seemed to magnify the color intensity. However they noticed that if the patch of green were placed next to a patch of red the color at the border seem to be intensified. This phenomenon was used by the Impressionists to good effect and was one of the principal ideas prompting the foundation of their school.
Josef Albers later expanded on these ideas in a series of paintings where the principle of field effects was exploited. You’ve probably seen optical illusions where a blue field will have a gray dot in the center. However this dot will appear slightly yellowish or greenish as the blue appears to project its opposite color into adjacent color fields. While this idea is simple to grasp in an optical illusion its application to painting is more difficult. But it can be exploited to good effect not only as a guiding principle to applying fields of color but also to adding color when you load your brush.
This principle can also be used when you paint zones of complementary colors. For example, if I paint a large green field the green is often difficult to control. So I might begin this area by painting a thin layer of red paint over the entire zone. The mingling of colors will begin to add a quality to the greens not achievable in any other way. I mingle the color somewhat haphazardly allowing some red to show between strokes and some layers of green to smear and mingle with the red. This mixture adds to the vibrancy of the paint surface. It is especially effective if I load my brush with plenty of purples and oranges to further accentuate a green in some places and neutralize it in others.
It may sound complicated, and I suppose it is, but with patience and practice you can achieve a quality of painting unequaled by any other method.