Mean metallicity uncertainties as a function of the magnitude of a star or its photometric metallicities for a random 1% of stars in the Pristine-Gaia synthetic catalogue (top) and the Pristine DR1 catalogue (bottom). Dots are color-coded by the G_BP – G_RP color of a star. The dashed regions corresponds to the regime for which metallicities might be hampered by systematics due to a stronger impact of the gravity of a star on its derived metallicity (see Section 6). The uncertainties are a complex function of the magnitude of a star, its color, and its metallicity because of the nontrivial mapping of metallicities on the color-color space shown in Figure 9. The metallicities based on Pristine magnitudes show much lower uncertainties owing to their significantly higher S/N.