A perceptibility study was conducted to visually determine the median tolerance values of 45 color-difference vectors in CIELAB color space using surface mode viewing of paint samples. Nine different color centers, each compris ing five color vectors, were employed to collect a superthreshold dataset. Fifty color-normal observers made quantal judgements under simulated Dg^ illuminant regarding the magnitude of color-difference pairs based on comparisons to a near-neutral color-difference anchor pair. Probit analysis was applied to the response frequencies for each vector to estimate the parameters of the distribution and the median tolerance values. Results indicated the probit adequately models the response distributions of the human observer population
