Color (or hue) is an obvious element in visual design, but here again; we find there is a sort of art science to its usage. Artists refer to what is known as color theory and the color wheel when discussing color.
By examining the color wheel, we can see how colors compliment and contrast each other. First we can identify the primary colors (red, yellow, and blue). Between the primary colors are the secondary colors (green, orange, and violet). Then between each primary and secondary color we have the tertiary colors (blue violet, yellow orange, etc.).
Artists learn how to use color theory to create proper color compositions. By referring to the color wheel they learn which color combinations work well together and which blend into hues that turn the stomach. We can also look to nature, the perfect example of color theory in motion, to further our understanding. Examine a sunset, a bird, a flower, or even a fish and notice how they each follow color theory, or rather perhaps, how color theory conforms to nature. If you would like to learn more about the basics of color theory you should check out this great resource that lays it out in a very understandable way: http://www.tigercolor.com/color-lab/color-theory/color-theory-intro.htm