  We describe an algorithm that measures self-consistently the relative galaxy
contribution in a sample of radio-quasars from their optical spectra alone.
This is based on a spectral fitting method which uses the size of the
characteristic 4000\AA~ feature of elliptical galaxy SEDs. We apply this method
to the Parkes Half-Jansky Flat Spectrum sample of Drinkwater et al. (1997) to
determine whether emission from the host galaxy can significantly contribute to
the very red optical-to-near-infrared colours observed. We find that at around
$2\sigma$ confidence, most of the reddening in unresolved (mostly quasar-like)
sources is unlikely to be due to contamination by a red stellar component.
