i′ − Ks vs. Ks colour − magnitude diagram for all GROND sources in the XMMU J0338.7 + 0030 region with flux detections in the i′,z′,Ks bands at a significance level  ≥ 1σ, whatever the classification of the source by Le Phare (i.e., stars are included). Photometric errors (1σ) are also shown. In each panel, candidate members of XMMU J0338.7 + 0030 are reproduced according to the corresponding panel of Fig. 15. Here the red short-dashed, solid and long-dashed lines represent the 1σ, 3σ and 5σ flux thresholds in the i′,Ks bands, respectively. The red dotted–short-dashed line represents the completeness limits in the i′,Ks bands, as obtained from Fig. 12. The black vertical dotted and horizontal long-dashed lines reproduce the characteristic magnitude of the Ks-band luminosity function of cluster galaxies at z ~ 1.2 (Strazzullo et al. 2006) and the i′ − Ks colour–selection threshold for EROs (Pozzetti & Mannucci 2000). As a reference, the blue solid and short-dashed lines reproduce the red sequences of the clusters RDCS J0910 + 5422 at z = 1.106 (Tanaka et al. 2008) and RDCS J1252.9 − 2927 at z = 1.24 (Tanaka et al. 2009), respectively. The candidate members of XMMU J0338.7 + 0030 that are classified as elliptical galaxies (red symbols in panel b)) populate a locus that is broadly consistent with the red sequences of the other two clusters.