In this paper, we present a fuzzy-set of parametric functions, which segment the CIELAB space into 11 regions, which correspond to the group of common universal categories present in all evolved languages as identified by anthropologists and linguists. The set of functions is intended to model a color-name assignment task by humans and differs from other models in its emphasis on the intercolor boundary regions, which were explicitly measured by means of a psychophysics experiment. In our particular implementation, the CIELAB space was segmented into 11 color categories using a triple-sigmoid function as the fuzzy-sets basis, whose parameters are included in this paper. The model's parameters were adjusted according to the psychophysical results of a yes/no discrimination paradigm where observers had to choose (English) names for isoluminant colors belonging to regions in between neighboring categories. These colors were presented on a calibrated CRT monitor (14-bit×3 precision). The experimental results show that intercolor boundary regions are much less defined than expected, and color samples other than those near the most representatives are needed to define the position and shape of boundaries between categories.