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.