The CMYK colour model, often referred to as ‘process’ colour or ‘four-colour’, is a subtractive colour model, used in colour printing. CMYK refers to the four inks used in most colour printing: cyan, magenta, yellow, and key (black).

The “K” in CMYK stands for key since in four-colour printing cyan, magenta, and yellow printing plates are carefully keyed or aligned with the key of the black key plate. Heavy black can be made from using all four plates at 100% strength, however text set in this way can often become unreadable due to plate alignment. Often text that has been saved in an RGB colour model (see below) and converted to CMYK will result in this.

The term Spot Colour means any special single colour not generated by a non-standard CMYK offset ink; such as a Pantone colour, metallic, fluorescent, spot varnish, or custom hand-mixed inks. UV coatings are sometimes referred to as 'spot colours', as they share the characteristics of requiring a separate lithographic film and print run.

The Pantone Color Matching System is largely a standardised colour reproduction system, meaning different manufacturers in different locations can all refer to the Pantone system to make sure colours match without direct contact with one another.

The Pantone system also allows for many 'special' colours to be produced such as metallics and fluorescents.

Most of the Pantone system's 1,114 spot colours cannot be simulated with CMYK, however their are translations for a screen based RGB colour system for monitor display.

The RGB colour model 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, though it has also been used in conventional photography. Before the electronic age, the RGB colour model already had a solid theory behind it, based in human perception of colours.

Typical RGB input devices are colour TV and video cameras, image scanners, and digital cameras. Typical RGB output devices are TV sets of various technologies (CRT, LCD, plasma, etc.), computer and mobile phone displays, video projectors, multicolour LED displays, etc. Colour printers, on the other hand, are not RGB devices, but subtractive colour devices (typically CMYK colour model).

CMYK model	RGB model

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