AbstractThe functional relation of visual to colorimetric scaling of small color differences is needed for a realistic interpretation of the perceptual magnitude of a measured color difference. Linearity is usually assumed and differences are expressed in threshold units without adjustment. an experimental plan is described that provides for the application of gray‐scale assessment to visual judgments under controlled parameters. Gray scale and test colors were produced from a two‐component acrylic lacquer system. A green color center (CIE green) was chosen for a first test with color differences extending from the center in the directions of hue, saturation/chroma, and lightness in steps ranging from ‐5 to + 5 thresholds. Thirteen observers made 4 judgments of each of 78 color‐difference pairs. the resulting scales were typically linear but increasing less steeply than threshold stepping; however, Fstatistics showed some inhomogeneous effects. Scales along the main color directions tended slightly to subadditivity. the vector model of color difference better predicted the magnitude of diagonal jumps between two color directions than did the city‐block model. Relations to some recent color‐difference formulae were studied and the CIE TCI‐29 formula was found to be a good predictor for this color center. © 1995 John W