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Colour Models
Many people from different fields of research have tried to explain colours and order colours during the last 2600 years.
Today, we can clearly define the colour models used in our time. On one hand there are the 
physical - technical models and on the other hand we can portray the perceptive oriented colour models.
Physical - Technical Models
When we talk about the physical – technical models, we are talking about models representing colours as ordered sets of numbers.
The most common colour models are the physiological, additive RGB system and the physical, subtractive CMYK system. The CIE, CIE- Lab and CIE-LUV systems may also be included in this group, but can be clearly differentiated by their description in space. That is to say,
they form a group of independent hardware and software colour models. RGB and CMYK are working within a 2-D rectangular co-ordinate
system whereas the CIE, CIE-Lab and CIE-LUV systems belong to the category of 3-D colour-ordering systems.
The question arising from this is:
Why do we need a 3-D colour system? In practice, the 3-D systems meet our needs to enable an objective description of any colour, also in light to dark gradations, that can't be met by 2-D co-ordinate systems.
Perceptive Oriented Models
Within the group of perception oriented colour models we need to mention, the HSL or so called HSB system, this is one of the systems you will often see when working with colour. HSL stands for Hue, Saturation and Lightness where, Hue is the base colour (from the wheel), Saturation is the purity, in fact how much grey is mixed with the colour and, Lightness is how much black or white is in the colour. In case of HSB, B stands for Brightness. This perceptive HSL model also works in a cylindrical 3-D co-ordinate system to describe colour tones. Have a look at the following animation operating in a 2-D co-ordinate system:
In addition to the colour ordering models, we can visualise dimensions in a colour-space. This space is described as a mathematical presentation of colour-valences. The bigger the colour-space, the larger the amount of presentable colours. The technical terminology for this colour-space is Gamut.
For further, optional information regarding this course, you can find on the internet-page:
Have a look at the animation to increase your understanding of how each colour model works:
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