Red, Green and Blue. This colour system cannot be used for planographic printing such as lithography, but is often used in digital printing, the files stay in this format. The actual inks in the printer however are still CMYK, often with the additional colours of light cyan, light magenta, an extra black and sometimes orange and green (called hexichrome) to give wider colour gamut and better tonal graduation. RGB are the primary colours of light, which are different to the primary colours of pigments in paints and inks.