Check out the graph of the light that is picked up by the 3 types of [https://en.wikipedia.org/wiki/Cone_cell](color cones) (top graph), turns out the wavelength picked by the green cones and the wavelength picked up by the red cones are actually pretty close, not opposite at all.
The brain normally figures out which color it sees by calculating how much light each type of cone receives. Red green blindness means the brain fails to interpret this distinction. A green light actually still activates the red cones, and vice-versa, but there’s less of a reaction, and the brain can’t compare that to the excitation of each type of cones correctly, so it just thinks that only one type of cone was excited, only a bit less. That’s why one color can be mistaken for the other, only more dull.
(disclaimer: not an eye-ologist)
Check out the graph of the light that is picked up by the 3 types of [https://en.wikipedia.org/wiki/Cone_cell](color cones) (top graph), turns out the wavelength picked by the green cones and the wavelength picked up by the red cones are actually pretty close, not opposite at all.
The brain normally figures out which color it sees by calculating how much light each type of cone receives. Red green blindness means the brain fails to interpret this distinction. A green light actually still activates the red cones, and vice-versa, but there’s less of a reaction, and the brain can’t compare that to the excitation of each type of cones correctly, so it just thinks that only one type of cone was excited, only a bit less. That’s why one color can be mistaken for the other, only more dull.