The OSA uniform color system is a 3-D collection of color samples according to the regular rhombohedral structure in which each color is surrounded by its 12 nearest neighbors, all perceptually equally different (local uniformity). The Swedish NCS system is a 3-D collection of color samples that vary gradually in each of the three perceptual attributes. It is not clear that this arrangement implies all neighboring pairs along the respective coordinates being perceptually equally different (local uniformity). Of pairs (j,k) of interest, predicted color differences djk were calculated that have the following property. Suppose an observer selects a pair of Munsell grays (Va, Vb) that matches in size with the color difference between (j,k), then djk=|Va-Vb| is predicted by djk, on the average, with error of 0.34 in Munsell V-unit. Variation of djk in this unit was in the order of 0.22V for nearest neighboring pairs (j,k) in various cleavage planes of OSA-UCS and in the order of 0.11V for neighboring pairs (j,k) along s-coordinate and c-coordinate in sheets with fixed hue of NCS. Both were well within the prediction error range, but some systematic trends in values of djk were found.