  Evolutionary models of elliptical galaxies are constructed by using a new
population synthesis code. Model parameters are calibrated to reproduce the
observed colour-magnitude (CM) relation of Coma ellipticals in $V-K$ vs.
$M_{V}$ diagram. The SEDs are degenerated in stellar age and metallicity. An
attempt is performed to break this degeneracy, by simulating evolution of the
CM relation of elliptical galaxies, based on the two alternative
interpretations; i.e., the CM relation reflects different mean stellar age or
various stellar metallicity. A confrontation with the CM diagrams of E/S0
galaxies in the two distant clusters Abell 2390 ($z=0.228$) and Abell 851
($z=0.407$) reinsures previous contentions that the CM relation is primarily a
metallicity effect. This conclusion does not depend either on the model
parameters, or on the cosmological parameters adopted.
