D_n4000 trend with redshift. The measurements for the single objects of the CCs sample are shown in grey; blue and red dots are median values averaged in two mass bins, log(M_⋆/M_⊙)≤10.88 (high-mass) and log(M_⋆/M_⊙) > 10.88 (low-mass), respectively. The different lines show the D_n4000–z relation obtained from the 2016 version of the Bruzual & Charlot (2003) models at different formation redshifts and assuming a reference flat ΛCDM cosmology (Ω_M = 0.3, Ω_Λ = 0.7 and H₀ = 70 km s⁻¹ Mpc⁻¹), purely for illustrative purposes. We note that, qualitatively, the observed trends follow the cosmological models quite well, but we defer to Sect. 4 the full cosmological analysis.