Color–magnitude diagrams of the five Galactic dSphs, shown as small grey dots. Dartmouth isochrones are overplotted as solid lines, for a fixed age of 12.5 Gyr, a range in metallicities from  −2.5 to  −1 dex, and a step size of 0.5 dex. The thick black dots correspond to the stars in common to the photometric and Ca T-based spectroscopic sample. The error bars correspond to the photometric errors. In the CMD of Sculptor, the red and blue asterisks indicate the location of the extremely metal-poor stars with a high-resolution iron abundance of  −3.96 dex and  −3.48 dex, respectively, identified by Tafelmeyer et al. (2010; red: Scl 07–50; blue: Scl 07–49), while the photometric metallicities obtained for the same stars are  −2.55 dex and  −2.71 dex, respectively. In the CMD of Fornax, again the red asterisk indicates the location of the extremely metal-poor star with a high-resolution iron abundance of  − 3.66 dex (Tafelmeyer et al. 2010; Frx 05–42), while the photometric metallicity assigned to the same star is  − 2.98 dex.