Colour–absolute magnitude diagrams (non-dereddened) of GES iDR5 SB1 candidates using Gaia DR2 parallaxes and photometry. Gaia constraints on relative parallaxes and photometry errors amount to 50% (left), 10% (middle), and 5% (right). The grey line depicts the main sequence for twin SB2 with q = 1, i.e. 0.75 mag above the main sequence. The top left arrow shows the direction of the reddening vector.