Colors are not necessarily a single wavelength, and the human visual system can't distinguish between identical "tristimulus" caused by a single wavelength or a mixture of wavelengths. This is why color monitors with red, green, and blue pixels work. The red, green, and blue are designed to stimulate your long, medium, and short wavelength receptors. Models like CIE1931 map wavelengths to tristimulus values, which your monitor then maps to the right intensity of its red, green, and blue. (Display technology is, of course, imperfect. You can see redder reds, greener greens, and bluer blues than your monitor can emit, though newer monitors with Adobe RGB or DCI-P3 have redder reds. It's also possible that the green light from your monitor is not perfectly stimulating only your medium wavelength receptors.)
Some colors that look very real cannot be a single wavelength of light, like magenta. That color is a figment of our imaginations. (Rather, there is no wavelength of light that stimulates your long wave receptors and short wave receptors without stimulating the medium wave receptors. But, magenta does, because it's actually a blue wavelength and a red wavelength.)
