> No, cones do not produce a negative response.

Yes, they do, after the photoreceptors. Those CIE colorspace curves aren't biology, and shouldn't be interpreted as such.

LMS colorspace is the (currently understood) biological colorspace [1], and contains inhibitions, from the opponent process [2] found in the meatware [3]:

red-green: L - M

blue-yellow: S - (L + M)

This contains a nice introduction to biological colorspace [4].

[1] https://en.wikipedia.org/wiki/LMS_color_space

[2] https://en.wikipedia.org/wiki/Opponent_process

[3] https://en.wikipedia.org/wiki/Lateral_geniculate_nucleus#Col...

[4] https://color2.psych.upenn.edu/brainard/papers/Stockman_Brai...