It is important to understand that there are two different colour systems: 'additive' and 'subtractive'. Coloured pigments, as in printed inks are termed 'subtractive'. The diagram on the right side show that when all 3 colours (RGB) are combined together they make a dark brownish colour, close to, but not quite black. Light on the other hand is an ‘additive’ system and when the three primary colours of light are mixed, white is produced.
One of the most common representations of a colour space is the 'colour wheel' shown here, which is used in many software programs to define or choose colours.
There are a number of different methods of accurately describing the colour of an object. The two most common methods are RGB which stands for Red, Green, Blue, which is very widely used in machine vision, and CMYK which stands for Cyan, Magenta, Yellow, Key which is the favoured method used in commercial printing. In addition to these there are HSL, (Hue Saturation Luminance), CIE Lab (Commission Internationale de l'Eclairage), and HSV, (Hue Saturation Variance), plus a number of others.
It should be noted that when using a colour space to determine absolute values for a colour inspection application such as print inspection, it is important to use a colour corrected light and camera combination.