  In a recent paper we presented the first semi-analytic model of galaxy
formation in which the Thermally-Pulsing Asymptotic Giant Branch phase of
stellar evolution has been fully implemented. Here we address the comparison
with observations, and show how the TP-AGB recipe affects the performance of
the model in reproducing the colours and near-IR luminosities of high-redshift
galaxies. We find that the semi-analytic model with the TP-AGB better matches
the colour-magnitude and colour-colour relations at z ~ 2, both for
nearly-passive and for star-forming galaxies. The model with TP-AGB produces
star-forming galaxies with red V-K colours, thus revising the unique
interpretation of high-redshift red objects as 'red & dead'. We also show that
without the TP-AGB the semi-analytic model fails at reproducing the observed
colours, a situation that cannot be corrected by dust reddening. We also
explore the effect of nebular emission on the predicted colour-magnitude
relation of star-forming galaxies, to conclude that it does not play a
significant role in reddening their colours, at least in the range of
star-formation rates covered by the model. Finally, the rest-frame K-band
luminosity function at z ~ 2.5 is more luminous by almost 1 magnitude. This
indicates that the AGN feedback recipe that is adopted to regulate the
high-mass end of the luminosity function should be sophisticated to take the
effect of the stellar populations into account at high redshifts.
