If you've ever struggled to develop an effective color scheme for a website, or wondered why banks, corporations, and financial institutions always bathe their sites in blue, you're not alone. Most Web developers understand the ins and outs of the web-safe color palette and the hexadecimal system, but the secret to choosing the right colors for a site often remains elusive.

For centuries, the nature of color itself was a veritable mystery. Ancient philosophers all proposed a variety of theories to illuminate how humans were able to see the world in vibrant color. Socrates, for instance, postulated that fire originating from the eye combined with an object's intrinsic whiteness to produce color. Later, Isaac Newton thankfully discovered the true relationship between color and light, and futher scientific research, continued well into the 20th century, led to a precise understanding of light waves and color perception.

Yet beyond a purely scientific examination of light and color, the study of both color harmony and the evocative properties of color has remained almost exclusively in the domain of the arts-- and Madison Avenue. This guide to color theory sheds light on some of the more enigmatic aspects of the effective use of color on the Web, and illustrates techniques you can use to reveal color harmonies and harness the power of color symbols.

Color Models and Management

When designers deal with color, they usually rely on one of two color models: the additive color model, in which individual color waves combine to form white light, or the subtractive model, in which pigments are used to subtract light waves. Both the traditional artist's palette and the CMY(K) systems are subtractive color models. On the Web, where we deal with light projection rather than light reflecting off of objects, we use an additive model called RGB.

In the natural world, the light waves that reach our retina are reflected off of objects, but there are other ways to produce color. Stage lights, for example, produce color by projecting and combining various light waves. Computer monitors also use projected light, but in this case the light is produced by firing electon guns against a phosper screen. These guns fire electrons in three colors: red, green and blue. Only these three are necessary to produce a full spectrum of color. Thus when we use color on the Web or any electronic medium, we combine these three colors together to create others. This is known as the RGB color system.

Within the RGB system, all other colors are derived from adding together these three primary colors. Combining two of the primary colors together produces three secondary colors: cyan, magenta and yellow. As previously noted, adding all three primary colors together produces white light. Thus an RGB value of 255,255,255 produces white. The complete absence of the three primary colors (RGB: 0,0,0) produces black.

The inverse of the RGB model is the CMY(K) model, in which light waves are subtracted to produce the desired color. Since the color of an object is derived from reflected light waves, this system uses three primary colors that each absorbs red, green or blue light. For instance, if you subtract red light, the remaining green and blue waves produce cyan. Thus the pigment used to subtract red light and reflect back green and blue appears cyan. Similarly, print designers use magenta to absorb a percentage of green light and yellow to absorb a percentage of blue.

At this point it should be apparent that the primary colors of the CYM(K) model are the secondary colors of the RGB model, and vice versa. Moreoever, if red, green and blue light combined produce white light, it stands to reason that cyan, yellow and magenta pigments should combine to create black, since they should absorb all of the light waves. However, due to the limitations of the pigments and the printing system, the full combination of cyan, yellow and magenta is not quite enough to absorb all light. In practice, it's necessary to add black to the system, hence the (K) in CMY(K).