  We present optical and IR integrated colours and SBF magnitudes, computed
from stellar population synthesis models that include emission from the dusty
envelopes surrounding TP-AGB stars undergoing mass-loss. We explore the effects
of varying the mass-loss rate by one order of magnitude around the fiducial
value, modifying accordingly both the stellar parameters and the output spectra
of the TP-AGB stars plus their dusty envelopes. The models are single burst,
and range in age from a few Myr to 14 Gyr, and in metallicity between $Z$ =
0.0001 and $Z$ = 0.07; they combine new calculations for the evolution of stars
in the TP-AGB phase, with star plus envelope SEDs produced with the radiative
transfer code DUSTY. We compare these models to optical and near-IR data of
single AGB stars and Magellanic star clusters. This comparison validates the
current understanding of the role of mass-loss in determining stellar
parameters and spectra in the TP-AGB. However, neither broad-band colours nor
SBF measurements in the optical or the near-IR can discern global changes in
the mass-loss rate of a stellar population. We predict that mid-IR SBF
measurements can pick out such changes, and actually resolve whether a relation
between metallicity and mass-loss exists.
