In the OSA-UCS (Optical Society of America-Uniform Color Scales), except for colors on the boundary of the three-dimensional solid (L, j, g), each color is surrounded by the 12 nearest neighboring colors that are supposed to be perceptually equally different (local uniformity). In the Swedish NCS (Natural Color System), colors are arranged so as to gradually vary in each of the three perceptual attributes: hue, phi; blackness, s; and chromaticness, c. The gradual change in an attribute may correspond to change of color difference from one to the next with a constant step (local uniformity). In each of these color-order systems, the uniformity was tested by a color-difference formula (d) over tilde based on color-component differences. When a coordinate is fixed (e.g., j in OSA-UCS, or c in NCS), a for neighboring pairs turned out fairly constant. However, systematic differences were found between (d) over tilde in one coordinate and (d) over tilde in another coordinate. (C) 2003 Wiley Periodicals, Inc.