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Color Models
When you ask children to tell you the names of all the colors, they'll know red, blue, yellow and a few more. A more sophisticated adult will be able to name periwinkle, mauve, fuchsia and maybe another hundred. There are, however, thousands of regularly used colors and millions more that can be distinguished by the human eye. To give a name to each of them would be impossible, so scientists have devised various ways of assigning numeric values to colors. These systems are called color models, and they provide precise methods for naming and reproducing exact colors. Some are based on the optical components of the colors and others are based on how people "feel" colors are related to each other.
RGB (RED, GREEN, BLUE) MODEL
In the RGB system, the red, green and blue dots are assigned brightness values along some scale, for example 0 to 255, where 0 is dark and 255 is bright. By listing the three values for the red, green and blue phosphors, you can specify the exact color that will be mixed.
Additive colors get lighter when mixed. As each component of light is mixed in, the combination becomes a new color.
Red, green and blue are the three additive primaries. You can mix any color of light with different combinations of the additive primaries. When you mix all three together in balanced amounts, you get white.
These three primaries are the basis of the additive color model. It's called the RGB model, and it's usually used to create color on your computer display as well as other electronic devices.
By mixing together various amounts of red, green and blue light, you can make almost any color. The RGB color space is a multi-colored cube with different points showing what colors different mixtures of red, green, and blue make. Television screens and computer monitors make their colors by mixing red, green and blue lights. A monitor or television screen mixes a color by illuminating tiny dots of red, green and blue phosphors with an electron gun located at the back of the monitor. By illuminating each of the dots to a different brightness, the monitor creates different colors.
The next several pages have descriptions of the major color models and some experiments to help you visualize how they work.
Because the RGB model is only capable of producing a certain range, or gamut, of colors, there are some colors that cannot be reproduced accurately by a computer monitor. The number of colors visible on a monitor is further reduced by the limitations of the video hardware in the computer, which may display anywhere from just black and white up to 16.7 million colors.
 Cyan, magenta and yellow are the three subtractive primaries. Nearly any color can be produced with different combinations of these three colors. When you mix all three together in equal amounts, you get a near black.
These three primaries are the basis of the subtractive color model. That's why it's called the CMY model. A close relative of the CMY model, called CMYK, is commonly used by printers and some software.
CMYK (Cyan, Magenta, Yellow, Black) Model
Many computer printers and traditional "four-color" printing presses use the CMYK model. In the CMYK model, by using cyan, magenta, yellow and black inks or paints, you can mix nearly any color.
In theory, you can mix any reflective color by mixing a combination of cyan, magenta and yellow. In the real world, however, the inks that printers use are not perfect. This becomes most obvious when you mix all three to make black. The color that results is muddy brown, due to impurities in the inks. That's why printers use black ink to get the best results.
Subtractive colors get darker when mixed. Each of the mixed paints or inks absorbs different components of the light. If the right combination of paints is mixed together, all of the components of light are absorbed and the result is a near black.
When preparing a color image for printing, the prepress operator makes four separation plates. Each plate is for one of the four colors of ink in the CMYK model. When all four plates are aligned and printed on top of each other, the inks will combine to simulate the proper colors. This method is referred to as "process color" (or "four-color") printing.
HSL (Hue, Saturation, Luminance) Model
The HSL model is very similar to the RGB model. In fact, when they're expressed mathematically, they're identical. The difference lies in how colors are expressed numerically.
The hue determines which basic color it is. Red, green, blue, yellow, orange, etc. are different hues. Saturation and luminance tell more about the variations of these basic colors. Saturation is the vividness (or "purity") of the color, i.e., how much of the color's complement is mixed in. Finally, luminance refers to the "whiteness" of the color. It may also be termed "brightness," "value" or "intensity."
Other models related to the HSL model are the HSB (Hue, Saturation, Brightness) and HSI (Hue, Saturation, Intensity) models. These terms are all similar but not interchangeable.
CIE (Commision Internationale l'eclairage) Model
The CIE model is a more subjective description than the others. In 1931, the Commision Internationale l'Eclairage tested many people and found that the sensitivity of the receptors in the eye caused certain colors to be associated with others. The CIE color space includes all visible colors, whether or not they can be defined in the RGB or CMYK models.
Computer printers and other devices for displaying color have practical limitations that prevent them from making ALL of the visible colors. The colors that they CAN create are collectively called the color gamut. The CIE model is useful in part because a printer's color gamut can be drawn on the CIE color space showing what colors cannot be printed.
Other color models closely related to CIE are UCS (Uniform Color Space), CIELAB and CIELUV.
PANTONE® COLOR REFERENCE SYSTEMS
The PANTONE MATCHING SYSTEM® is a solid color communication system based on the visual matching of individual, pre-mixed colors. The PANTONE MATCHING SYSTEM is a series of books with thousands of precisely printed colors alongside printers' formulas for mixing those colors.
The PANTONE MATCHING SYSTEM is used by artists and commercial printers to select, specify and match colors very precisely. Many logos are created with specific PANTONE Colors that can be very closely reproduced. By using PANTONE Colors, designers can be confident that their output will match their expectations.
The original PANTONE MATCHING SYSTEM included 504 colors and has since been expanded to include 1,012 colors along with their printing ink formulations. For four-color (CMYK) printing, the PANTONE Process Color System® specifies more than 3,000 colors and shows the screen percentages for printing.
Recently, as computers have been used more extensively for business and professional graphics, software users have begun to specify their colors with the PANTONE MATCHING SYSTEM and the PANTONE Process Color System. More and more software products have been licensed by Pantone, Inc. to ensure a greater degree of consistency throughout the industry.
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