Additive & subtractive colour models

There are two main types of colour models, additive and subtractive.

Additive colour models are used when blending light to produce colour.
The primary colours for most additive models are red, green, and blue (RGB).
When combined at full intensity, they produce white light.
The additive RGB model (and HSB colour model) is central to display technologies such as computer screens, TVs and phone screens.
The additive spectral colour model is particularly useful for developing an understanding of the relationship between wavelengths of light within the visible spectrum and corresponding colours.
Additive models are based on the way human eyes perceive colour, with each colour being produced by a combination of different wavelengths. In contrast, a subtractive model is based on the way pigments reflect light.

Subtractive colour models are used when working with pigments, inks and dyes.
The primary colours for most subtractive colour models are cyan, magenta, and yellow (CMY).
When combined cyan, magenta, and yellow produce black.
The subtractive CMY colour model and CMYK colour model are central to printing technologies.
In practice, the CMY colours often can’t produce a perfect black when mixed due to impurities in the pigments or inks, so a fourth ‘Key’ component (represented as K) is often used in printing to produce a true black.