Color matching and acceptability measurements were made on a visual colorimeter for chromaticities of CIE standard illuminants A, D55, D65 and D75. It was found that the matching and acceptability tolerances of the 4 illuminants took the shape of ellipses on the CIE 1931 chromaticity diagram. The acceptability tolerance ellipses of these illuminants were then plotted on the CIE 1960 UCS diagram and CIE 1976 (L*u*v*) space and they all turned out to be more circular in shape. However, the illuminants A and D6B were more oiroular on the CIE 1976 space, whereas D55 and D75 were more circular on the CIE 1960 diagram. Thus, from the shapes of the acceptability tolerance of the 4 CIE standard illuminants, it is not possible to tell that the CIE 1976 (LW) space is more uniform than the CIE 1960 IJCS diagram.