Colours have many different referencing systems. The following are probably the only ones that you will ever need to know about, from a printing perspective.
RGB
This is the Red, Green and Blue system used to create the colour spectrum on computer monitors and TVs. It works by blending set percentages of the Red, Green & Blue, which then create all the other colours. However this only works for light based colours. It is most commonly used by web designers and cannot be used for printing with ink pigments on paper. For that one of the following two systems must be used.
CMYK
This is the Cyan, Magenta, Yellow and Black system, used to create the colour spectrum when using full colour printing. It works by printing layers of the CMYK dots on top of one another in different percentages of intensity, to create the illusion of all the colours of the rainbow. However it only works with pigment based inks and not light.
Pantone Spot Colours
When printing in one or two colours, people usually do not want to go to all the expense of using the full colour CMYK system. So they use a Pantone spot colour. This system works by giving every colour in the spectrum an individual reference number and for that reason it has the widest color range of them all. It goes from metallic inks to fluorescent.
Rather than creating the illusion of the color you want by laying down different layers of dots, your printer will mix up a tin of ink that is exactly the right colour you requested. Much in the same way that you would buy a tin of paint off the shelf in a DIY shop. It is an unadulterated colour that cannot be used in any other way. This colour is then put on the printing press and everything is printed in it.
