  Colours of spiral galaxies generally are affected by the underlying old
stellar population, younger stars, and extinction by dust. Old and young
populations generally can be disentangled using a combination of blue and
near-infrared colours. Extinction effects are very hard to take into account,
except for galaxies with special orientations. In this paper we give some
results of one of the first studies of galactic bulges and disks in various
optical and near-infrared bands, and its implications for the stellar
populations of spirals.
