Rest-frame U − V versus V − J diagrams showcasing galaxies in different environments Upper left: galaxies that are members of the over-densities identified in CDFS excluding the two that host passive galaxies. Upper centre: members of the proto-cluster at z = 3.55. Top-right: members of the proto-cluster at z = 3.43. Lower left: field galaxies associated with the proto-cluster at z = 3.55. Bottom-right: field galaxies associated with the proto-cluster at z = 3.43. The colour scale denotes log(sSFR) provided by BEAGLE, with red signifying lower values and blue higher ones. Different symbols represent galaxies with a spectroscopic redshift (triangles), galaxies with a photometric redshift (dots), AGNs (diamonds), and passive galaxies (creen crosses). The lines in the diagrams outline the classification criteria set by Williams et al. (2009), we used for the passive galaxy selection, and Whitaker et al. (2011), shown for comparison.