An attempt has been made to explain how dichromatic confusion lines can be used in building a model for color vision. In the König color vision model the fundamental colors are located on the mixture diagram at the copunctal points for protanopes, deuteranopes, and tritanopes. In Fry's model the copunctal points fall on the alychne and cannot represent the fundamental colors. On a constant luminance diagram the confusion lines for the different dichromats are sets of parallel lines. This arrangement of the confusion lines can be explained in terms of a zone theory of color vision.