A linear model for representing reflectances has been developed from a group of 5574 samples of acrylic paint on paper Using acrylic paints makes easy the generation of a large variety of samples by mixing, due to the high miscibility among these kinds of pigments: this point was the key to achieve a great spatial homogeneity in our samples. Besides, these kinds of paints keep their chromatic properties stable over time. The first 7 vectors of the so-called overall linear basis were sufficient for a more than adequate mathematical representation of the spectral-reflectance curves. A study by hue groups of the mathematical properties of these curves indicates that the nse of a hue basis of representation implies, on the average, a reduction in 1 or 2 of the number of vectors needed in order to achieve results analogous to those of the over-all basis.