Full Colour Printing: 4 colour printing

The CMYK colour process (process colour, four colour), used by most professional printers is a subtractive color model,  and is also used to describe the printing process itself. CMYK refers to the four inks used in some color printing: cyan, magenta, yellow, and black.

The CMYK model works by partially or entirely masking colors on a lighter, usually white, background. The ink reduces the light that would otherwise be reflected. Such a model is called subtractive because inks “subtract” brightness from white.

In additive color models such as RGB, (which is used for most computer monitors) white is the “additive” combination of all primary colored lights, while black is the absence of light. In the CMYK model, it is the opposite: white is the natural color of the paper or other background, while black results from a full combination of colored inks.

The difference between addictive and subtractive colours can represent a big difference in your colour reproduction, so you should never trust a monitor when it comes to the proofing and printing of colours, you should always ask for a colour proof printed on the paper you will be using.
Instead of using a 4 colour process made up from Cyan, Magenta, Yellow and Black, you can use a 1 colour, 2 colour or 3 colour process. This will print a particular reference colour (for example Pantone Colours). These colours tend to be very vibrant and accurate to published standards. They are extensively used for stationery printing, and if a logo has to be an exact colour.
1 colour, 2 colour and especially 3 colour print is being superceeded by the 4 colour process, which is often cheaper for bulk quantities, but sheffield printing company 221 print, www.221print.com still use these methods to great effect.