A colour wheel is a diagram based on a circle divided into segments and used to explore the effect of mixing adjacent colours.
- A colour wheel is a perceptual tool used to explore a colour model.
- Colour models that use colour wheels include:
- RGB colour model – Used for mixing light.
- RYB colour model – Used for mixing opaque pigments
- CMY colour model – Used for mixing semi-transparent inks.
- Colour wheels are not used to explore the spectral colour model because each colour corresponds with a single wavelength of light rather than mixtures of primary colours.
- The spectral colour model is usually portrayed as a strip of colours with red at one end and violet at the other.
- 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 circular diagram divided into segments, featuring primary colours, and used to visualize the result of colour mixing.
- Colour wheels can enhance understanding of colour relationships and assist with the accurate selection and reproduction of colours.
- A colour wheel starts with segments representing primary colours. Additional segments are added between them to explore the outcome of mixing adjacent primary colours.
- By adding more segments between existing ones, further mixing of adjacent colours can be explored.
- A colour wheel exploring the additive RGB colour model starts with red, green, and blue primary colours.
- A colour wheel exploring the subtractive CMY colour model starts with cyan, magenta, and yellow primary colours.