Pygmalion's Art Tutorials: About Color Schemes: Complementary
This color scheme is created from two colors that are opposite of each other on the color wheel. This scheme looks best when you put a warm color against a cool color, for example, red versus cyan. The complementary scheme is intrinsically high-contrast and sets up tension.
When using the complementary scheme, it is important to choose a dominant color and use its complementary color for accents. Using one color for the background and its complementary color to highlight important elements, you will get color dominance combined with sharp color contrast.
Find below, a screen shot from the Kuler web site to see an example of a complementary color scheme.
The six color schemes are: Monochromatic, Analogous, Complementary, Split Complementary, Triadic and Tetradic. Make sure you review all of them to get a complete understanding of color schemes.

