Colour wheels are used to represent colour models that can generate a complete range (gamut) of colours using three primary colours. These models include:
The RGB colour wheel
The RYB colour wheel
The CMY colour wheel
The spectral colour model, which represents individual wavelengths of light in the visible spectrum, is not typically explored using colour wheels.
A diagram of the spectral colour model typically depicts its constituent colours in the form of a strip with red at one end and violet at the other.