The Difference between RGB (red, green, blue) and CMYK (cyan, magenta, yellow and black) color printing is:
RGB is a display color mode used to create every other tone that is visible on your computer monitors and television screens. Even though each screen is capable of displaying a wide range of colors, there are still inconsistencies between screens.
CMYK is a printing color mode, used for traditional offset and digital printing. The four colors (cmyk) combined to create the color spectrum used in printing. CMYK printing does not reproduce color the same way that you view color on your RGB computer monitor.
The technique used to print full-color images, such as color photographs, is referred to as four-color-process or merely process printing. By printing four distinct dots of color, one black, one cyan, one yellow and one magenta you are able to see these as four separate colors. When one partially overlaps these four colors, in various amounts of overlap, you create an enormous color gamut.
Color printing typically uses ink of four colors: cyan, magenta, yellow and key (black). When CMYK “primaries” are combined at full strength, the resulting “secondary” mixtures are red, green and blue. Mixing all three theoretically results in black, but imperfect ink formulations do not give true black, which is why the additional K component is needed.
Inks used in color printing presses are semi-transparent and can be printed on top of each other to produce different hue. For example, green results from printing yellow and cyan inks on top of each other. However, a printing press cannot vary the amount of ink applied to particular picture areas except through “screening,” a process that represents lighter shades as tiny dots, rather than larger dots, which create darker areas of ink.