Colours in your computer are usually represented by three numbers that represent proportions of red, green and blue light.

When mixed, these will correspond to a particular colour we see. This is based on the way our colour vision works and gives what are known as RGB values. But what are these colours? What does the 'red' number in an RGB value represent?

Well, there are standards which define ways of measuring colours and can give absolute values and meaning to the numbers in a RGB value.

These numbers are completely independent of any device (screen or printer) that may be used to display the colours represented.

However, consider your computer monitor - does its version of red match up with a standard? No, and what's more, if you have a second monitor, its red probably won't match the first one.The red (or any other colour) produced by your monitor is said to be 'device dependant'. One 'R' value may produce one colour red on one monitor and a different version on another.What about your printer? Here it's even more difficult, since you are trying to reproduce red from coloured inks, none of which is (usually) red.

How do I even know that my camera has captured the 'correct' colour red?

Colour management is all about trying to relate all these device dependant colours to standards in a consistent useful way.

It's about trying to make sure that the picture I took of the red bus looks correct on my screen, your screen, my printer and your printer -- and they all match (as best as they can) to the bus I saw in the street at the time.

Typically, things called 'icc profiles' provide the translation between what an actual physical device can do, and the standards.Colour management helps you get colour right more often...It does get a bit more complicated though