On the assumption of a color space of constant negative curvature, von Schelling has given simple formulas for the color metric coefficients. An attempt has been made to fit such formulas to newly available color-discrimination data for 12 normal observers. A least-squares analysis indicates that Y should be replaced with the quantity, Y′ = Y-0.085X+0.011Z, in the special role assigned to luminance by von Schelling. Corresponding to this change, coordinates x’=X/(X+ Y’+Z), y’= Y’/(X+ Y’+Z) yield the simplest formulas for the coefficients of the expression for color difference: ΔS=(g₁₁Δx’²+2g₁₂Δx’Δy’+g₂₂Δ′2+g₃₃ Δy²/y²)½. Least-squares fitting of the experimental data to von Schelling’s formulas yielded: g₁₁=g₃₃/(10x’2-6.886x’+2.083+2.5y’-16.66x’y’+19.6y’²). g₁₂=g₁₁(0.3443-x’)/y’. g₂₂=g₁₁[0.09+(0.3443-x’)²]/y’². These formulas are the best approximations obtainable on the assumption of a color space of constant negative or zero curvature. However, they give such poor approximations to the experimental data that it is concluded that the assumption of a color space inherently more complicated than a space of constant curvature would be required to fit the data to a closeness commensurate with the experimental reproducibility.

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