Colour–colour diagrams for various samples used in DSC. Top: training data for quasars (blue) and galaxies (orange). Middle: Gaia sources assigned classlabel_dsc=‘quasar’ (blue) and classlabel_dsc=‘galaxy’ (orange). Bottom: Gaia sources assigned classlabel_dsc_joint=‘quasar’ (blue) and classlabel_dsc_joint=‘galaxy’ (orange). The differences in the distributions are due to the various levels of completeness and purity in the two types of class label.