Additive colour

Additive colour refers to the way two or more wavelengths of light can be combined to produce other colours.  the RGB colour model, HSB colour model and Spectral colour model involve different additive methods to produce systematic ranges of colour.

About additive colour
  • Additive colour is the method used to mix wavelengths of light, whilst subtractive colour is the method used when mixing pigments such as dyes, inks and paints.
  • An additive approach to colour is used to control the emission of light by the screens of televisions, computers and phones.
  • The additive approach to colour is also used by digital projectors which reflect wavelengths of light off a white surface towards an observer.
  • A colour model can be thought of as a theory of colour whilst additive colour or subtractive colour refers to the method used in practice.
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 simply by combining the light emitted by arrays of red, green and blue pixels (picture elements) in different proportions.

  • RGB colour is an additive colour model that combines wavelengths of light corresponding with red, green and blue primary colours to produce other colours.
  • Red, green and blue are called additive primary colours in an RGB colour model because just these three component colours can produce any other colour if mixed in the right proportion.
  • Different colours are produced by varying the intensity of the component colours between fully off and fully on.
  • When fully saturated red, green and blue primary colours are combined, they produce white.
  • A fully saturated colour is produced by a single wavelength (or narrow band of wavelengths) of light.
  • When any two fully saturated additive primary colours are combined, they produce a secondary colour: yellow, cyan or magenta.
  • Some RGB colour models can produce over 16 million colours by varying the intensity 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.