Gaia (BP - RP) colour versus brightness temperature, T_B, for SMGPS-X-ray matches with RASS and eRASS1 detections. Markers represent stellar classifications reported in SIMBAD. The interacting binaries include the RS CVn, eclipsing, and spectroscopic binaries. Evolved stars comprise classical cepheids and long-period variables. The G-type, K-type, and M-type classifications are based on the Gaia astrophysical parameter catalogue (Gaia Collaboration 2023). The vertical error bars show the propagated uncertainties from the flux measurements and distances.