Colour–colour diagram for sources in the qso_candidates table, excluding regions around the LMC and SMC. Left column: shows sources with classlabel_dsc = quasar (2.77 million sources), the right column: shows sources with classlabel_dsc_joint = quasar (the purer subset, 0.52 million sources). These numbers refer to the number of sources plotted, which are those that have all Gaia bands. Upper panel: mean DSC-Combmod probability for the quasar class (the field classprob_dsc_combmod_quasar). Lower panel: density of sources on a log scale relative to the peak density in that panel (densities 1000 times lower than the peak are not shown).