Host galaxy contribution to the colours of 'red' quasars

We describe an algorithm that measures self-consistently the relative galax y contribution in a sample of radio quasars from their optical spectra alon e. This is based on a spectral fitting method which uses the size of the ch aracteristic 4000 Angstrom feature of elliptical galaxy spectral energy dis tributions. We apply this method to the Parkes half-Jansky flat-spectrum sa mple of Drinkwater et al. to determine whether emission from the host galax y can significantly contribute to the very red optical to near-infrared col ours observed. We find that at around 2 sigma confidence, most of the redde ning in unresolved (mostly quasar-like) sources is unlikely to be the resul t of contamination by a red stellar component.