Metallicity trend with effective temperature for all spectra with log g < 4.4 (i.e. stars between the TO and the tip of the RGB) and S/N> 50. Overplotted with a solid red line are the mean values and standard deviations of the metallicity in 250 K wide bins. The same is plotted again with a dashed red line including a correction (Lind et al. 2012) for NLTE effects (with the same uncertainties). Overplotted in blue is an isochrone including atomic diffusion (Richard, priv. comm.). See text for details.