Color-magnitude diagram of 161 CB candidates drawn from matching eRASS1 – Gaia sources (blue symbols) shown on the left. The background is made of ∼230 000 unrelated Gaia sources with π/σ_π > 100 (π: parallax). X-ray to optical flux ratio (log f_X + phot_g_mean_mag/2.5 + 4.86) vs. optical colour of eRASS1 sources matching with Gaia within a radius of 1 arcsec, shown on the right. The lower branch on the right figure is populated by coronal emitters, the upper branch by AGN and accreting binaries. The position of J1912-44 is marked red in both diagrams and the 161 Gaia candidates in blue.