neuroscience - If people with colorblindness lack one type of cone cells, shouldn't they be unable to recognize one particular color?

The 3 types of cone cells in normal humans allow them to view 3 types of colors and any color made from mixing and matching those 3.

So, 2 types of cone cells should only allow to view just 2 types of colors and any colors made from those two.

But that is clearly not the case.

https://en.wikipedia.org/wiki/Color_blindness#Red.E2.80.93green_color_blindness

Protanopes, deuteranopes, and tritanopes are dichromats; that is, they can match any color they see with some mixture of just two primary colors (whereas normally humans are trichromats and require three primary colors).

Also, from personal experience, I'm colorblind and can see and differentiate all 3 red, green, and blue. It's just the hues between red-green and green-blue I can't distinguish much...

How exactly do dichromats see all three colors when they lack one type of cone cell?

Answer

Cones do not literally interpret colors. The three cones work together to encode a signal that is abstractly interpreted by your brain in higher processing centers. Here is what neuroscientists currently think the decoding scheme looks like:

This leads to what's called opponent process, an antagonist mechanism whereby the perception of green/red are a matter of the contrast between the two. In a deuteranopes, the mechanism of antagonism is missing, so the colors can not be differentiated.

What this implies is that (to some extent) a single color has no meaning. Colors are only meaningful in the context of other colors.