De-reddened stacks, according to the same colour code as in Fig. 13, scaled by their mean emission between 1770 Å and 1810 Å. For comparison, the VB01 template is also shown in black as an external reference, rather than the usual L20 template. The rising continuum slopes with increasing redshift (and extinction) are clearly observed. Inset: UV continuum slopes of the literature samples described in Section 4.1 and plotted in Fig. 4 (squares), against the slopes of the de-reddened spectra (dashed lines).