No device – whether it be your computer monitor, digital printing, offset printing, etc – is capable of producing all of the colors a human eye can see. Each device works within a specific “color space” which makes up a certain gamut of colors.
Colors can shift in appearance from one device to another because of the variety of color spaces. These variations can result from differences in image sources; the way software applications define color; print media; and even the age or manufacturing difference of your monitor.
RGB and CMYK
RGB is an additive process. Your monitor translates an image into pixels that are then projected as rays of red, green and blue light. Not all monitors are exactly the same so you will experience variations from one monitor to another.
RGB color spaces are generally larger than CMYK spaces and are becoming more popular to use when jobs are sent to the printer. Larger color spaces are able to produce more and brighter colors. RGB also presents itself for a greater range of output such as web, digital (think email here) or print.
Most print devices use CMYK inks, so at some point a conversion from RGB will take place, most often by the printer.
CMYK is a subtractive process. Cyan, magenta, and yellow ink is placed on white reflective paper. Each then absorbs, or subtracts, its opposite color from the white light reflected back. Black is used to change the colors luminosity value (light to dark).
Typically CMYK color spaces have a gamut of color smaller than RGB spaces. This translates to fewer and less vivid colors. The RGB colors you created are often beyond the range of CMYK to reproduce and will come out darker and more dull in print than what you saw on your on-screen display. To accurately print the document, it must be converted to CMYK. CMYK delivers color consistency if a project is to be spread between multiple print devices (think distribute and print or print at the point of consumption).
Conversion from RGB to CMYK can be a complex task. It is recommended you speak with your printer; many times they are more than happy to make the conversion for you.