Data obtained for color defective individuals will show a clustering of maximum errors in two regions which are nearly opposite on the hue circle. A line drawn through these two points is referred to as the confusion axis. The orientation of the confusion axis can be used to identify the type of color defectiveness.
To aid diagnosis, typical confusion axes for protan deutan and tritan defects can be superimposed on the polar graph by selecting the Show Confusion Axes option.
See Also Identifying Color Vision Deficiencies