This is the most important point. How we perceive a color depends not only on the distributions of wavelengths, but also on the surroundings. See, for example, this image, where the two squares on the Rubik's cube are actually the same RGB pixel values:The additive colour 'wavelength' is subjective, i.e. as interpreted by the viewer's brain.
by Aaron Carman
by Jake Hertz
by Duane Benson