Temperatures and surface gravities from our training sample (left) and their behavior in the Pristine color-color space for giants (log 𝑔 < 3.9; middle panel) and dwarf stars (log 𝑔 > 3.9 or T_eff > 5, 800 K; right-hand panel). The synthetic color resulting from synthetic spectra for stars with [Fe/H] = 𝑔3.0 (blue) and (hypothetical) stars with no heavy metals (black) are overplotted with larger star symbols. Stars are plotted from the most metal-rich to the most metal-poor, so as to emphasize the metal-poor region. The sharp edge at log g ~ 3.9 in the left panel is due to the APOGEE sample that is limited to giants only (see text). The very low-metallicity stars from Aguado et al. (2019) have less physical log g determinations, showing up as horizontal lines in this panel. However, this does not significantly affect their metallicity, or location in the color-color space (see Aguado et al. 2019, for a detailed discussion). The magnitudes shown here are de-reddened following the procedure described in Section 4.