The color spectrum shows the order in which visible light appears in nature. When pure white light shines though a prism it will separate in to the visible spectrum below.

In color theory, the color wheel is a spectrum which has been joined end to end. Color wheels show how visible colors are related to each other. Primary, secondary, and intermediate colors are organized on a circular chart, like the one below. This tool may seem simple, but it's indispensable to designers. Once you know how it works, you can glance at a color wheel to see which colors compliment each other, which ones clash, and which colors will create the perfect color effect.