CMYK and RGB
Four colour printing, also known as full colour or CMYK, is the most common form of printing.
Four primary inks, Cyan, Magenta, Yellow and Black (Key) are printed onto a sheet in a pattern of tiny dots that is perceived as a solid colour.
The combination of these dots creates the illusions of many more colours.
RGB is an additive colour model in which red, green, and blue light are added together in various ways to reproduce a broad array of colours.
The name of the model comes from the initials of the three additive primary colours - red, green and blue.
The main purpose of the RGB colour model is for the sensing, representation and display of images in electronic systems, such as televisions and computers, not for use in printing.
Artwork files should not be supplied as RGB but should be converted to CMYK (or to specific PMS colours if the job requires it).