Additive colour and the RGB colour model

The RGB colour model used by TV, computer and phone screens involves additive colour mixing.

The RGB colour model produces all the colours seen by an observer on TV, computer and phone screens by creating arrays of red, green and blue pixels (picture elements) in different proportions.
Red, green and blue are called additive primary colours in an RGB colour model because just these three component colours alone can produce any conceivable colour if blended in the correct proportion.
Different colours are produced by varying the brightness of the component colours between completely off and fully on.
When fully saturated red, green and blue primary colours are mixed in equal amounts, they produce white.
A fully saturated hue is produced by a single wavelength (or narrow band of wavelengths) of light.
When any two fully saturated additive primary colours are mixed, they produce a secondary colour: yellow, cyan or magenta.
Some implementations of RGB colour models can produce millions of colours by varying the brightness of each of the three primary colours.
The additive RGB colour model cannot be used for mixing pigments such as paints, inks, dyes or powders.

The RGB colour model does not define the exact hue of the three primary colours so the choice of wavelengths for each primary colour is important if it is to be used as part of a colour-managed workflow.
The RGB colour model can be made device-independent by specifying a colour profile such as sRGB or Adobe RGB (1998) which ensures consistent results regardless of the device used to output an image.