Unlike red, green, or blue, purple does not correspond to a single wavelength of visible light. It does not appear in the natural spectrum produced when light is split by a prism or seen in a rainbow.
Scientists describe purple as a non-spectral colour. This means it cannot be found in the natural sequence of light wavelengths. The visible spectrum includes red through violet, but not purple.
The perception of purple results from the human brain processing both red and blue wavelengths at the same time. Instead of showing them separately, the brain blends the signals to form a new colour.
Colours such as seafoam green or burnt umber are also non-spectral. These hues do not correspond to any single
Although violet appears at the end of a rainbow, purple does not. That’s because there is no place in the spectrum where red and blue light mix naturally, making purple absent from the rainbow’s display.
The visible light spectrum is a limited part of the full electromagnetic range. Colours beyond violet (ultraviolet) and red (infrared) exist but cannot be seen by the human eye without the help of instruments.
According to the European Space Agency, combining visible, ultraviolet, and infrared images reveals a more extensive "rainbow" than what human vision allows. This shows that visible light is only a small part of the full spectrum.