Bands of colour, spectral and non-spectral colours

Bands of colour are composed of a continuous range of wavelengths, so for example:
- A continuous range of wavelengths between 750 – 620 nanometres (nm) typically appear red to an observer.
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- Wavelengths between 590 – 570 nm will typically appear yellow.
- A continuous range of wavelengths between 450 – 380 nm will typically appear violet.

A spectral colour is a colour that is evoked by a single wavelength of light (or narrow band of wavelengths) within the visible spectrum.
Spectral colours are the colours red to violet.
Diagrams of the spectral colour model are linear and may show colours selected:
- Using equal and incremental steps in wavelength.
- According to equal and incremental steps in the appearance of colours.

Non-spectral colours are produced by additive mixtures of wavelengths of light.
Examples of non-spectral colours produced by two spectral colours are:
- Purple – produced by mixing wavelengths corresponding with red and violet. Red (740nm) and violet (400nm) are at the extreme limits of the visible spectrum.
- Magenta – produced by mixing red (660nm) and blue (490nm).
- Mauve – produced by mixing orange (600nm) and blue (450nm).
- Examples of non-spectral colours produced by three spectral colours are:
  - Tints
  - Greys
  - Shades
  - So all achromatic colours are non-spectral colours.
Whilst both spectral and non-spectral colours are produced by mixing a combination of colours corresponding with different wavelengths of light:
- The RGB colour model produces a full gamut of colours by mixing red, green and blue primary colours in different proportions.
- The CMY colour model produces a full gamut of colours by mixing cyan, magenta and yellow primary colours in different proportions.