D_n4000 trend with redshift. In grey, we show the measurements for the single objects of the CCs sample; blue and red dots are median values for objects with log(M_⋆/M_⊙)≤10.86 (high-mass) and log(M_⋆/M_⊙) > 10.86 (low-mass), respectively; similarly, blue and red stars are measurements obtained on stacked spectra of low- and high-mass samples. In the background, lines refer to evolutionary models from Bruzual & Charlot (2003) at different formation redshifts.