RGB composite image of the 1.4′ × 1.4′ field centred on the CL J1449+0856, as in Fig. 1. The R, G, and B channels correspond to the K_s,J, and Y bands, respectively. The Y, J, and K_s photometry straddles wavelengths close to the 4000 Å break at z ~ 2 and is useful to appreciate likely age variations among potential cluster members. The red arrows show the positions of red galaxies with photometric redshifts within 2σ of the peak of the distribution and the blue ones the position of galaxies with spectroscopic redshifts within 2σ of the peak. The green square gives the position of the AGN seen with Chandra. The white ellipse shows the 20′′ semi-major axis region that corresponds roughly to the overdensity and from which were selected the red galaxies shown in Figs. 7 and 10 and in Table 2.