Evolutionary tracks for various ZAMS masses obtained from the BoOST SMC (gray dashed lines; Szécsi et al. 2022) stellar evolutionary tracks, together with the corresponding isochrones interpolated for selected ages (colored solid lines). In this set of stellar evolutionary tracks, cases where two stars along the same isochrone may exhibit T_hot > 12 000 K, T_cool < 8000 K, and L_hot/L_cool ≥ 2 arise only at ages ≲3 Myr, where the isochrones curve back towards high T_eff (red and blue lines) due to blueward evolution along the M_ZAMS > 55 M_⊙ tracks.