Strength of the 4000 Å break as a function of stellar mass. The mean D_n(4000) value for the star forming galaxies in the comparison clusters, in bins of stellar mass, is shown with the thick blue lines. The thick red lines show the same for the passive members of the comparison clusters. The shaded regions in cyan and magenta show the standard deviation around the mean values for the star forming and passive galaxies, respectively. The A 520 galaxies are split into three groups. The star forming ones are shown with blue stars, the passive ones with empty red circles and the recently quenched ones with green diamonds. The last group contains the passive galaxies with D_n(4000) lower than the average of the star forming ACReS galaxies with the same stellar mass. The number of passive and star forming galaxies in the comparison clusters is indicated in each stellar-mass bin.