Illustration of a few spectral domains where T_eff-sensitive flux ratios have been recovered: a) blue wing of Hβ, b) MgT region, c) metallic lines around 5510 Å, d) H I line in the near-infrared. See Sect. 4.4 for details. Spectra are color-coded by temperature, where darker colors indicate cooler temperatures. For illustration purposes, the spectra were pseudo-normalized by the 99th percentile of the flux in the presented range.