  We present optical and near-infrared colour maps of the central regions of
bulges of S0 and spiral galaxies obtained with WFPC2 and NICMOS on the HST. By
combined use of HST and ground-based data the colour information spans from a
few tens of pc to a few kpc. In almost all galaxies the colour profiles in the
central 100-200 pc become more rapidly redder. We attribute the high central
colour indices to a central concentration of dust. We infer an average
extinction at the center of A_V = 0.6 - 1.0 mag. Several objects show central
dust rings or disks at sub-kpc scales similar to those found by others in giant
ellipticals. For galactic bulges of types S0 to Sb, the tightness of the B-I vs
I-H relation suggests that the age spread among bulges of early type galaxies
is small, of at most 2 Gyr. Colours at 1 R_eff, where we expect extinction to
be negligible are similar to than those of elliptical galaxies in the Coma
cluster, suggesting that these bulges formed at the same time as the bright
galaxies in Coma. Furthermore the galaxy ages are found to be independent of
their environment. Since it is likely that Coma was formed at redshift z > 3,
our bulges, which are in groups and in the field, also must have been formed at
this epoch. Bulges of early-type spirals cannot be formed by secular evolution
of bars at recent epochs, since such bulges would be much younger. There are
three galaxies of type Sbc and later, their bulges are younger and could
perhaps arise from secular evolution of transient bars. Our results are in good
agreement with semi-analytic predictions (Baugh et al. 1996, 1998, Kauffmann
1996), who also predict that bulges, in clusters and in the field, are as old
as giant ellipticals in clusters.
