Photoreceptors and light with mixed frequencies
Yes, current color models assume a linear response in the spectrum.

Given a light with mixed spectrum $\Phi(\lambda)$, the response of a cone with spectral sensitivity $\Psi_i(\lambda)$ is a (nonlinear) function of the L2 inner product:



This is how CIE XYZ color space is defined.

Reference:


M. D. Fairchild. Color Appearance Models, 3rd edition. 2013 (p.63)
https://en.wikipedia.org/wiki/CIE_1931_color_space