Color-magnitude diagrams (CMDs) of globular clusters reveal the presence of multiple sequences likely due to populations of stars with different chemical composition (variations in He, C, N, O, Na, Mg, Al). We present synthetic photometry of the globular cluster NGC 6752 based on isochrones and atmosphere models both consistently taking into account such variations of chemical composition. Theoretical CMDs based on this photometry are compared to observed CMDs. We show that CMDs based on red filters are reasonably well reproduced, while those based on blue filters suffer from a number of shortcomings.