The Difference Between ‘Violet’ and ‘Purple’ (2015)

When a mixture of photons that have different wavelengths hits the retina (creating a ratio of red, green, and blue activation different from any spectral colour), the brain will perceive it as an entirely different colour. You can have a source of monochromatic violet light (i.e. a source producing just a single wavelength), but everything that looks purple must emit both red and blue light. Purple is a mixture of red (which is at the opposite side of the spectrum than violet) and blue (which is relatively far from violet), so it is, in terms of wavelengths, a completely different colour.

Source: jakubmarian.com