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 of primary colours 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.
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 is well suited 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.
  • The RGB color model used in digital displays and imaging devices is based on the trichromatic nature of human vision.
About trichromatic colour vision (Trichromacy)

Trichromatic colour theory explains how the human eye perceives colour.

  • Trichromatic colour theory is based on the existence of three types of light-sensitive cone cells in the retina, each responsive to a different range of colours.
  • The colours we perceive result from the combined responses of all three types of cones.
  • The sensitivity of cone cells forms the physiological basis for trichromatic colour vision in humans.
  • The ability to see colour stems from interactions among the three types of cones, with each cone exhibiting a preference for specific wavelengths within the visible spectrum.
  • The three cone types are denoted by the initials L (responsive to long wavelengths), M (responsive to medium wavelengths), and S (responsive to short wavelengths).
    • L-type cones exhibit the highest responsiveness to light with long wavelengths, favouring wavelengths around 560 nm.
    • M-type cones exhibit the highest responsiveness to light with medium wavelengths, favouring wavelengths around 530 nm.
    • S-type cones exhibit the highest responsiveness to light with short wavelengths, favouring wavelengths around 420 nm.
Related diagrams

Each diagram below can be viewed on its own page with a full explanation.

References

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.