A) Stellar metallicity of ETGs, as a function of M_⋆, predicted by our model (orange to red) and observed at z ~ 0 and z ~ 0.7 (Gallazzi et al. 2006, 2014) (black line with gray scatter, and green lines with dashed uncertainty envelope). For comparison, the stellar metallicity of SF galaxies at z = 0 is shown in blue. B) M_⋆ to bolometric light ratio (M/L) for z = 0 passive galaxies (solid line), with respect to the Salpeter case (dotted line). The red dots and green squares show, respectively, spectroscopic observations of low-redshift ETGs from Cappellari et al. (2013) and Spiniello et al. (2014). For consistency, we have converted M_⋆ into velocity dispersions using Eq. (5) in Cappellari et al. (2013).