Consequently, one of the peculiarities of red-‐green deficiencies is that blue and yellow colors appear to be remarkably clear compared with red and green colors. But the part of spectrum which appears to those with protanopia as grey, appears to those with protanomalia as a grayish indistinct color, and likewise, the grey part of the spectrum seen by the person with deuteranopia appears to those with deuteranomalia as a indistinct color close to grey. In protanomalia and deuteranomalia, there is not part of the spectrum, which appears grey. Purple-‐ red, which is the complementary color of green, appears also as grey. The visible range of the spectrum is not contracted, in contrast to protanopia. In deuteranopia, this zone into two areas, each of which appears to be of one system of color, divides that part of the spectrum, which appears to the normal as green, appears as grey, and the visible range of the spectrum. The red with a slight tinge of purple, which is the complementary color of blue-‐green, appears also as grey. Each area appears to those with protanopia as one system of color with different brightness and saturation within each area, the color in one area being different from that of the other. The whole visible range of the spectrum in protanopia consists of two areas, which are separated from each other by this grey part.
In protanopia the visible range of the spectrum is shorter at the end compared with that of the normal, and that part of the spectrum, which appears to the normal as blue-‐green, appears to those with protanopia as grey.
Most cases of congenital color vision deficiency are characterized by a red-‐green deficiency which may be of two types first, a protan type which may be complete (protanopia) or partial (protanomalia), and, second, a deutan type which may be complete (deuteranopia) or partial (duteranomalia). This is the commonest form of color vision disturbances.