Color-color diagrams of the potential host galaxies associated with FXTs 16, 18, 19, 20, 21 and 22 (colored stars), “distant” FXTs from Paper I (magenta hexagons), and X-ray sources classified as stars in Paper I (gray filled circles) and here according to Criterion 2 in Sect. 2.7.2 (black filled circles). The expected parameter space of stars with different ages [log(Age) = 7.0 − 10.3], metallicities ([Fe/H] = −3.0 − 0.5), and attenuations (A_V = 0.0 − 5.0) taken from the MIST package (Dotter 2016; Choi et al. 2016) are overplotted as cyan regions.