Distribution of the CALIFA mother sample in the u − z vs. M_z colour-magnitude diagram. The overplotted numbers indicate the number of galaxies in bins of 1 mag in M_r and 0.75 mag in u − z. Different colours and symbols represent a classification into bulge- and disk-dominated galaxies as well as intermediate cases, as suggested by the concentration index C. For comparison, the contours delineate the number density distribution of galaxies in the SDSS-NYU catalogue (e.g., Blanton et al. 2005).