Left and middle panels: magnitude in the F814W filter as a function of the magnitude difference in the F275W and F814W filters (left) and the color index C_438W (middle). The symbols denote the stars in the synthetic cluster. The red and blue lines in each panel are the fiducial lines used to calculate color differences in the chromosome map. Right panel: chromosome map. For clarity, the different populations are color-coded according to their initial chemical composition. Colors are the same as in Fig. 1.