The relationship between the equivalent width (EW) of the first four Balmer lines and Gaia G_BP − G_RP color for both the original model grid (left, represented by solid curves) and the interpolated BestFit models corresponding to each MaStar spectrum (right, represented by points color-coded by log g). The EW-color distribution of the set of MaStar spectra, with extinction effects removed, is shown in the background of each panel in gray.