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.
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?