(1) Dichromatism may have been lost repeatedly within the dabbling ducks, and thus it is possible that monochromatism is the derived state in Grey Teal (vs. dichromatism in the other taxa).(2) The genetic cause has been determined for several color vision defects, achromatopsia (the loss of all color vision), blue monochromatism , protanopia, deuteranopia, and enhanced S-cone syndrome.
