Ten modelled SEDs are plotted for each source (reconstructed from 10 randomly-picked realisations of the posterior PDFs) as transparent red (red QSOs) and blue lines (control QSOs) to display the uncertainties. Solid red and dotted blue lines depict the composite median SED for the red and control QSO population respectively, matched in redshift and L_6 μm. At frequencies log ν < 14.5 Hz, strikingly similar composite SEDs can be observed for the red and control QSO populations. At frequencies log ν > 14.5 Hz a clear difference in the composite SEDs can be observed which is the signature of dust reddening consistent with the optical colour selection.