Colour wheel

A colour wheel is a diagram based on a circle divided into segments and used to explore the effect of mixing adjacent colours.

  • The minimum number of segments in a colour wheel is three with a primary colour in each.
  • Segments between primary colours are used to explore the result of mixing adjacent pairs to produce secondary colours.
  • Segments between secondary colours can be used to explore the result of mixing further pairs of adjacent colours.
  • Wheels of increasing complexity are produced by further subdivisions.
  • The colours produced between the primary colours in a colour wheel are called secondary colours.
  • The colours produced between the secondary colours are called tertiary colours.
  • Colour wheels used to explore additive and subtractive colour models start with different sets of primary colours.
    • An RGB colour wheel, used to explore additive mixing of light, starts with red, green and blue primary colours.
    • An RYB colour wheel, used to explore subtractive mixing of pigments starts with red, yellow and blue primary colours.
    • A CMY colour wheel, used to explore subtractive mixing of printing inks starts with cyan, magenta and yellow primary colours.

A colour wheel is a diagram based on a circle divided into segments. The minimum number of segments is three with a primary colour in each. Segments added between the primaries can then be used to explore the result of mixing adjacent pairs of primary colours together. Additional segments can then be added between all the existing segments to explore the result of mixing further pairs of adjacent colours.

  • The human eye, and so human perception, is tuned to the visible spectrum and so to spectral colours between red and violet. It is the sensitivity of the eye to this small part of the electromagnetic spectrum that results in the perception of rainbow colours.
  • Colour wheels are often used in technologies which reproduce colour in ways that match the light sensitivity of the three different types of cone cells and the rod cells in the human eye.
  • Colour wheels exploring additive colour models and subtractive colour models use different sets of primary colours.
  • An RGB colour wheel, used to explore additive mixing of light, starts with red, green and blue primary colours.
  • The colours produced in between the primary colours in a colour wheel are called secondary colours.
  • The colours produced in between the secondary colours in a colour wheel are called tertiary colours.
  • A CMY colour wheel, used to explore subtractive mixing of pigments and inks (used in digital printing) starts with cyan, magenta and yellow primary colours.
  • An RYB colour wheel used to explore the subtractive mixing of art pigments and paints starts with red, yellow and blue primaries.
  • The colour wheels described above all depend on trichromatic colour vision which involves three receptor types (cone cells) processing colour stimuli.
About colour models and colour wheels
  • Colour wheels are used to explore colour models that can derive a complete range (gamut) of colours from three primary colours. These models include:
    • The RGB colour wheel
    • The RYB colour wheel
    • The CMY colour wheel
  • Colour wheels are not used to explore the spectral colour model because each spectral colour corresponds with a single wavelength of light.
  • A diagram of the spectral colour model shows a strip of colours with red at one end and violet at the other.
About wavelengths of light and colour vision

There is a clear difference between the wavelengths of light that make up the visible spectrum and how the human eye converts the information it receives about wavelength into the perception of colour.

  • The human eye, and so visual perception, is tuned to the visible spectrum and so to spectral colours between red and violet.
  • It is the sensitivity of the eye to this small part of the electromagnetic spectrum that results in the perception of colour.
  • Photosensitive cone cells embedded in the retina of each eye respond to wavelengths of light corresponding with spectral colours.
  • Explained in simple terms, cone cells distinguish between different colours by determining how much red, green and blue are present when stimulated by their corresponding wavelengths.
  • The system used by the human eye to distinguish colours is called trichromacy or trichromatic colour vision.
  • The spread of wavelengths that the spectral colour model is concerned with lend themselves to a linear arrangement with the shortest at one and the longest at the other.
  • The way the human eye determines colour from the presence of three primary colours (red, green and blue) lends itself to a circular, wheel-like arrangement.
About trichromatic colour vision (Trichromacy)
  • The trichromatic colour theory is concerned with the system the human eye uses to see colour.
  • Trichromatic colour theory is based on the presence of three types of light-sensitive cone cells in the retina at the back of our eyes, each sensitive to a different spread of colour.
  • All the colours we observe result from the simultaneous response of all three types of cones.
  • The sensitivity of cone cells is the physiological basis for trichromatic colour vision in humans.
  • The fact that we see colour is, in the first instance, the result of interactions among the three types of cones (L,M and S), each of which responds with a bias towards its favoured wavelength within the visible spectrum.
  • The result is that the L, M and S cone types respond best to light with long wavelengths (biased towards 560 nm), medium wavelengths (biased towards 530 nm), and short wavelengths (biased towards 420 nm) respectively.