Confusion Lines

Confusion lines are the lines in a color space on which the colors cannot be discriminated by the corresponding dichromat (a person missing one photo-pigment). The red, green and blue dots and the confusion lines originated from them are that of protanope (missing long wavelength cone), deuteranope (missing middle wavelength cone) and tritanope (missing short wavelength cone) respectively. 

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Here the copunctal points derived by Smith and Pokorny (1975) are used because they are probably the only set of copunctal points for 1931 CIE color matching functions.   The spacing of the confusion lines are arbitrary. Please see Stockman, A., Sharpe, L.T. (1999) for a thorough review of cone primaries. Colblindor has a very readable blog explaining copunctal points and confusion lines.