In this study, we propose a color mixing and color separation method for opaque surface made of the pigments dispersed in filling materials. The method is based on Kubelka-Munk model. Eleven different pigments with seven different concentrations have been used as training sets. The amount of concentration of each pigment in the mixture is estimated from the training sets by using the least-square pseudo-inverse calculation. The result depends on the number and type of pigments selected for calculation. At most we can select all pigments. The combinations resulted with negative concentrations or unusual high concentrations are discarded from the list of candidate combination. The optimal pigment's set and its concentrations are estimated by minimizing the reflectance difference of given reflectance predicted reflectance. (c) 2008 Wiley Periodicals, Inc. Col Res Appl, 33, 461-469. 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20441