  In this study we present a simple model of elliptical galaxies aimed at
interpreting the gradients in colours and narrow band indices observed across
these systems. Salient features of the model are the gradients in mass density
and star formation and infall of primordial gas aimed at simulating the
collapse of a galaxy into the potential well of dark matter. Adopting a
multi-zone model we follow in detail the history of star formation, gas
consumption, and chemical enrichment of the galaxy and also allow for the
occurrence of galactic winds according to the classical supernova (and stellar
winds) energy deposit. The outline of the model, the time scale of gas
accretion and rate of star formation as a function of the galacto-centric
distance in particular, seek to closely mimic the results from Tree-SPH
dynamical models. Although same specific ingredients of the model can be
questioned from many points of view (of which we are well aware) the model
predictions have to be considered as a gross tool for exploring the
consequences of different receipts of gas accretion and star formation in which
the simple one-zone scheme is abandoned. With the aid of this model we discuss
the observational data on the gradients in metallicity, colour, and narrow band
indices across elliptical galaxies.
