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The purpose of this paper is to show the first results of a program designed to construct population models of stellar systems on the basis of theoretical data of stellar evolution. Synthetic HR diagrams were obtained using the isochrones and luminosity functions of Ciardullo and Demarque (1977). This last work is based on the stellar models of the Yale - IBM research group (Mengel, Sweigart, Demarque and Gross 1978; Sweigart and Gross 1976; 1978). The conversion from the theoretical HR diagram to observable parameters is made with the help of theoretical model stellar atmospheres principally due to Kurucz (1976), Relyea (1976) and Bell and Gustafsson (1975). The program provides a synthetic C-M diagram and integrated properties for the system given the following parameters: the chemical composition in terms of the (Y,Z) pair, the age, the total number of stars, the initial mass function (IMF) and the law of mass loss from stars in the system. In this brief paper, we shall concentrate on the integrated properties of theoretical star clusters and then remark on some interesting consequences for the color evolution of elliptical galaxies.