  We present a novel approach to draw the synthetic color-magnitude diagram of
galaxies, which can provide - in principle - a deeper insight in the
interpretation and understanding of current observations. In particular, we
`light up' the stars of chemical evolution models, according to their initial
mass, metallicity and age, to eventually understand how the assumed underlying
galaxy formation and evolution scenario affects the final configuration of the
synthetic CMD. In this way, we obtain a new set of observational constraints
for chemical evolution models beyond the usual photospheric chemical
abundances. The strength of our method resides in the very fine grid of
metallicities and ages of the assumed database of stellar isochrones. In this
work, we apply our photo-chemical model to reproduce the observed CMD of the
Sculptor dSph and find that we can reproduce the main features of the observed
CMD. The main discrepancies are found at fainter magnitudes in the main
sequence turn-off and sub-giant branch, where the observed CMD extends towards
bluer colors than the synthetic one; we suggest that this is a signature of
metal-poor stellar populations in the data, which cannot be captured by our
assumed one-zone chemical evolution model.
