A look at why it's so hard to achieve color consistency across different media.

Have you ever wondered why a client was fine with a design layout when viewed on your Web site then later irate when seeing it in print? The problem could be color consistency, which can be hard to achieve across different media.

Images viewed on your computer monitor will not have the same color when they come out of your printer - or your clients' printers, for that matter. Why? Because, not only is every monitor and printer different, but how color is created on a monitor versus how it is created on a printer is completely different. They speak different color languages and map color using different values. This is why you should frequently remind your clients that color matching using more than one media can be an exercise in frustration.

The science behind the why

Computer monitors, digital cameras, scanners and TVs use the RGB color space. Red, green and blue, the primary colors of light, are combined additively to produce a desired color. A computer monitor is capable of mixing millions of shades of RGB to create rich colorful pictures.

Printers and printing presses, on the other hand, use the CMYK color space. Tiny dots of the primary colors of pigment - cyan, magenta, yellow and black - are placed next to each other to create the optical illusion of different colors.

The two spaces behave in direct opposition to each other. For example, to display black on a computer, all three sources of RGB color are removed. For white, maximum amounts of all three are added. Contrast that with the printing process where, on a white piece of paper, equal amounts of all three colors combine to create black and their absence creates white.

Herein lies the rub

Unlike the RGB color space, the CMYK color space produces a much more limited range of colors. What does this mean in terms of color accuracy? It means it is possible to see RGB colors on your computer that you just can't replicate in print. These colors are said to be out of the CMYK color gamut. When your RGB file is translated to CMYK for printing, any colors that fall outside of the gamut will not be reproduced. Instead, the printer will substitute a CMYK color it considers closest. So, your crisp blue sky could turn out looking an alarming purple.