It’s actually very common. The obvious place most red/green colourblind people will have issues is differentiating red from green where the cones (would normal

It’s actually very common. The obvious place most red/green colourblind people will have issues is differentiating red from green where the cones (would normally) overlap, but with only two cones if you saturate both of them equally there’s no additional signal to tell if you’re looking at a colour or white light. The point at which a red-blind person’s green sensitivity intersect with blue is cyan, and for a green-blind person it’s green-cyan (turquoise), so depending on the tone/shade of turquoise it appears white to most colourblind people.