Left panel: histograms of stellar mass as estimated by LE PHARE for all z_phot members of the PCl J1001+0220 proto-cluster (left panel) and only those z_phot members with redder rest-frame colors (, right panel) plotted against the corresponding coeval field sample. Such a color cut selects galaxies with ages in excess of 200 Myr (see Fig. 7). All spectroscopic knowledge is ignored when defining these samples. Photo-z membership is defined by the projected radial cut given in the top left of the panel and 4.53 − 1.5σ_NMAD(1 + 4.53) < z_phot < 4.60 + 1.5σ_NMAD(1 + 4.60) with the remaining galaxies in this z_phot range comprising the coeval field sample. Histograms in both panels are normalized such that they contain the same area. While the two distributions shown in the left panel are formally consistent, once a color cut is imposed, the two distributions are found to be disparate at a >3σ level, with redder z_phot proto-cluster members exhibiting a preference for significantly higher masses relative to the coeval field.