A large number of the visible color spectrum can be represented by mixing the three primary colors, Red, Green and Blue, known as the RGB color model. This model is the one used by most computer monitors, TV screens, graphics cards and lighting effects. Mixing different amounts of each of the red, green or blue, creates different colors, and each can be measured from 0 to 255. If all red, green and blue are set to 0, the color is black, is all are set to 255, the color is white.

The CMYK color model is based on printing and ink absorbing into paper. To gain the greatest number of printable colors, from the fewest number of inks, CMYK color printing is used. By using varying amounts of Cyan, Magenta, Yellow and Black, a great number of colors can be printed. Most full color printed materials, magazines, posters, packaging, are printed using just the 4 CMYK inks. Here the level of ink is measured from 0% to 100%. As an example, orange would be represented by 0% Cyan 50% Magenta 100% Yellow and 0% Black.

Whereas most 'on screen' color is based on the RGB model, most full color printing is based on the CMYK model. One of the main principles to understand is that some colors can only be represented by RGB, and cannot be replicated by the CMYK process. Images may look bright, with full saturation on screen, however the color may be out of the range of the CMYK process. This is why images may look far different when on screen to when printed.

So when would I use each model? All 'on screen' images are RGB, whether it's for web pages, multimedia or games. CMYK is usually only used for full color printing on a printing press, or possibly for printing to a desktop color printer.

An image can be converted from RGB to CMYK using a program such as Adobe Photoshop, then re-saved as a CMYK version, or it can be done via a desktop printer at the time of printing. An RGB image printed to a desktop CMYK color printer will be converted to CMYK by the printer, at the time of printing, to allow it to print.