Please note: The images you see on your monitor will always look somewhat different than the final printed piece. Monitors / Screens display colour with light, while offset / digital presses print with ink. There are going to be varying differences in the visual results of printed matter. This is an unfortunate but expected result of CMYK printing.
RGB stands for Red, Green and Blue. These are the primary colours of light. By mixing the light values, you get colours. You start with black, and as you mix them all you get white (light). RGB colour is used by devices that emit light, such as computer screens, TVs, phones or LCD screens.
RGB: primary colours of light
CMYK is the standard colour system used for printing. When we mix Cyan, Magenta, Yellow and Black inks, we create colours. As the CMYK inks overlap each other on the paper, they eventually go from white (paper) to black.
CMY: primary colours of ink
Please note: Since RGB uses light and not ink, it is physically impossible to print RGB files without first converting them to CMYK, which is based on blending ink instead of light. Where colour accuracy is critical, we strongly recommend investing in a printed sample to avoid disappointment.