  We investigate the origin of the colour-magnitude relation (CMR) followed by
early-type cluster galaxies by using a combination of cosmological N-body
simulations of cluster of galaxies and a semi-analytic model of galaxy
formation (Lagos, Cora & Padilla 2008). Results show good agreement between the
general trend of the simulated and observed CMR. However, in many clusters, the
most luminous galaxies depart from the linear fit to observed data displaying
almost constant colours. With the aim of understanding this behaviour, we
analyze the dependence with redshift of the stellar mass contributed to each
galaxy by different processes, i.e., quiescent star formation, and starburst
during major/minor and wet/dry mergers, and disk instability events. The
evolution of the metallicity of the stellar component, contributed by each of
these processes, is also investigated. We find that the major contribution of
stellar mass at low redshift is due to minor dry merger events, being the
metallicity of the stellar mass accreted during this process quite low. Thus,
minor dry merger events seem to increase the mass of the more luminous galaxies
without changing their colours.
