Stellar metallicity [Fe/H] for i) all stars bound to the main galaxy (solid black lines); ii) accreted stars (solid red lines); iii) and outer stellar halo (dashed blue lines), as a function of total stellar mass (left panel) or virial mass (right panel). The dotted magenta line shows the mass-metallicity relation reported by Kirby et al. (2013). Simulated metallicities have been shifted downwards by −0.26 dex to match the Kirby et al. (2013) relation at M_* = 10⁹ M_⊙. Note the steep mass-metallicity of the accreted component, as well as the fact that outer stellar haloes have a substantial radial metallicity gradient. The outer haloes of dwarf galaxies should be fertile hunting grounds for metal-deficient stars.