The Missing Wavelength

Many colors in a rainbow correspond to a specific wavelength of light. Red sits at about 700 nanometers, violet at 380. Between those two extremes, the visible spectrum runs smoothly through orange, yellow, green, blue, and indigo.

But not every color you perceive has its own single wavelength. Some colors are non-spectral: they come from your brain combining signals from multiple cone types rather than from one pure frequency of light.

Scan that spectrum end to end and you will not find magenta anywhere. It does not have a wavelength. It does not correspond to any single frequency of light. Magenta is a color that exists only because your brain invented it.