Color contrast is defined by the comparison of, and differences between, certain colors. Complementary colors are those that aesthetically contrast when used in close proximity. This is a key color theory concept that is universally practiced by most knowledgeable painters. True complementary colors are those that are located opposite each other on the color wheel. For example, cyan blue is the complement of red, magenta for green, and yellow for dark blue.
Complementary colors become most effective when they produce maximum color contrast.
You need only compare bright yellow next to dark blue to observe how the two colors seem to visually vibrate as you gaze at it. This phenomenon is called simultaneous contrast, meaning that when we see a particular color, we also need to simultaneously see its complementary color. This effect can be used to either visually enhance or reduce the saturation of adjacent colors. Another important aspect of complementary colors is how they affect foreground objects. This is most apparent when you place a light-colored foreground object within a yellow background.