T_eff vs. cluster age. Top: ⟨ T_eff⟩ – the mean of the difference between BSS T_eff and MSTO T_eff, found with the same method, for stars within the same cluster – vs. cluster age. Blue triangles and red dots represent T_eff obtained from color-temperature relations for OCs and GCs, respectively. Green plus symbols (+) and orange squares represent T_eff derived from isochrone models for OCs and GCs, respectively. At the top right corner we show the results only for GCs without error bars for a better appreciation, keeping the same axes from the major plot. Error bars along vertical axis show the dispersion of BSSs T_eff. Middle: difference between ⟨ T_eff⟩ and the MSTO T_eff, normalized by the MSTO temperature. Horizontal gray dashed line indicates BSS T_eff=1.5 × MSTO T_eff. Bottom: dispersion of BSS T_eff vs. cluster age.