1. Wavelength discrimination for the colorblind is entirely determined by saturation differences in the spectrum. From the neutral point to the short-wave end, his spectrum may be completely matched by 440 mmicro plus white; to the long-wave end by 650 plus white. The proportion of color to white, hence the relative saturation, changes rapidly in the region of small Deltalambda at the center, and slowly in regions of large Deltalambda at the ends. 2. The data of spectrum gauging with two primaries (color mixture) by the dichromat are shown to contain the saturation distribution in the spectrum for the dichromat. This is because each mixture of primaries may be considered as composed of a mixture which matches white and of an excess of one primary. The data when so computed yield saturation distributions almost identical with those found by direct measurement, and show that on each side of the neutral point the basis of color mixture for the colorblind lies in saturation and not in hue differences. 3. To judge by these measurements, the spectrum for the protanope and deuteranope is composed of only two hues, themselves probably of low saturation, situated one at each end. Toward the center these hues decrease still more in saturation until they completely disappear in the white of the neutral point.