Wavelength Sensitivity of Cones in Human Eye

The curves below show the cone responses for the three types of cones in the human eye: B, G and R.

Relative sensitivity curves for the three types of cones log vertical scale, cone spectral curves from "On the derivation of the foveal receptor primaries" by J.J. Vos and P.L. Walraven (1971) Vision Research 11, 799-818.

Note that the response curves largely overlap one another - in particular the R and G curves - which is the fundamental reason why there can be different choices when selecting and defining "primary" colors .

Reference:
light and the eye by Bruce MacEvoy at handprint media