This is also not how it works: "Almost no one has a blue deficiency. Accordingly, nearly everyone can see blue, or, more accurately, almost everyone can distin

This is also not how it works: "Almost no one has a blue deficiency. Accordingly, nearly everyone can see blue, or, more accurately, almost everyone can distinguish blue as a color different from others." People with "red-green colorblindness" usually have difficulty telling purple from blue.