Six independent Geneva color–magnitude diagrams of HR 4049. The linear-regression fit to the data is shown in black. The other curves show the color/magnitudes of the Kurucz model, reddened with the interstellar extinction law of Cardelli et al. (1989, foreground extinction) and with different dust species with a grain size of 0.01 μm and an appropriate range of column densities (variable circumstellar extinction). The grain shape distribution is DHS with f_max = 0.8, except for amorphous carbon (Mie, i.e., DHS with f_max = 0). Top left panel: the discrepancy between the observed and the modeled U − B color may be due to a UV-excess in the binary system.