  Using data from the Sloan Digital Sky Survey (SDSS) it has recently been
shown that the red fraction of satellite galaxies increases with stellar mass.
Semi-analytical models, however, predict red satellite fractions that are
independent of stellar mass, and much higher than observed. It has been argued
that this discrepancy owes to the fact that the models assume that satellite
galaxies are instantaneously stripped of their hot gas reservoirs at the moment
they are accreted into a bigger halo. In this letter we show that the fraction
of red satellites can be brought in better agreement with the data by simply
decreasing this stripping efficiency. However, this also results in a red
fraction of massive centrals that is much too low. This owes to the fact that
the massive centrals now accrete satellite galaxies that are bluer and more
gas-rich. However, if a significant fraction of low mass satellite galaxies is
tidally disrupted before being accreted by their central host galaxy, as
suggested by recent studies, the red fractions of both centrals and satellites
can be reproduced reasonably well. A problem remains with the red fraction of
centrals of intermediate mass, which is likely to reflect an oversimplified
treatment of AGN feedback.
