By scientific definition, complementary colors are those opposite each other on the standard color wheel. The color wheel has the three primary colors–red, blue and yellow–spread equidistant around its circumference. The spaces between the primary colors contain secondary and tertiary colors, resulting in a wheel with many different versions of red, blue and yellow. Colors that are located directly across the wheel from each other are considered complementary.
Obtain a sample color wheel. You may find one at your local paint store, but a detailed image in a book, in a magazine or on a website will work just as well. Make sure your wheel is divided into at least 12 sections–called a “tertiary wheel”–so you will have ample choices for a pair of complementary colors.
Choose a wall color from the wheel. This will be the main wall color for the room. The final color does not have to be as intense as the color on the wheel, but at this point it is important to make a choice from the one of the twelve colors on the wheel.
Use the color wheel to come up with the opposite color, but be aware that a primary color will always have a secondary color as its complementary color and vice versa. The selected color will now become the main hue for your baseboard and trim areas. Now you have two contrasting colors that can be applied to the main wall and the smaller trim area.
Know the moods of the main colors. For the primaries red is the opposite of green, blue is the opposite of orange and yellow is the opposite of purple. These are strong color combinations even when one of the colors is used sparingly. So if you are not into bright color, now is the time to sit down with the rectangular blocks of paint colors that is supplied by the paint store and choose a pair of opposite colors that perhaps are toned down slightly from the pure color of the wheel. Even by choosing a mild shade or tint of a primary color and its complement, the vitality involved in these selections should still be plenty evident after the paint is applied.