Colour is colour, right? Wrong! Depending on your application and use, there are two main colour referencing formats you will come across: RGB and CMYK. These two colour formats are for completely different uses, but the result of the two formats is the same to our eyes.
 

RGB: the primary colours of light

RGB is an acronym for Red, Green and Blue: the primary colours of light. When your computer monitor or television screen reproduces images, the three primary colours are mixed together in varying shades and strengths. The important distinction here is that light, rather than ink, is used to reproduce an image. Just because a picture looks one way on a monitor or television screen does not mean that it will be reproduced accurately on paper.
 

CMYK: the primary colours of ink

CMYK is an acronym for Cyan, Magenta, Yellow, and Black: the primary colours of ink. When your printer reproduces images, the four primary colours of ink are mixed together in varying shades and strengths.

You are probably noticing the pattern about now, in that RGB and CMYK do the same thing but in different ways. What you have to understand is that RGB references light and CMYK is ink.

What all of this means.

You cannot print in RGB and you cannot view pictures on a monitor in CMYK. So, to answer our first question of how to know when you are using which colour format, monitors display in RGB and printers display in CMYK.

A conversion process has to take place to go from viewing pictures on a monitor to viewing the same pictures in print. What's more, the conversion is not always perfect or accurate. As to how this affects colour printing: there may be differences between what you see on the monitor and what you get back from the print shop. You can compensate for this by calibrating your monitor and through printing proofs to make sure your work is translating properly.

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