J − Ks versus Ks (top) and i − Ks versus Ks (bottom) CMDs of the inner region of XDCP J0044.0-2033 for galaxies at cluster-centric distances ≤13′′ (red circles) with a statistical cluster membership of 75% and objects within 13−30′′ (green circles) with a purity of 50%. Spectroscopic (tentative) members outside 30′′ are indicated by black circles, small dots mark all other galaxies in the field. Secure (tentative) spectroscopic members are marked by orange/cyan (black) squares with cyan indicating the presence of an [O ii]-emission line. The 100%/50%/10% completeness limits are shown by the solid/dashed/dotted black lines. The dashed green line in the top panel depicts the red-sequence location of XMMU J2235.3-2557 at z = 1.39 from Lidman et al. (2008) as reference. Horizontal dashed lines mark solar metallicity SSP-model color predictions for formation redshifts of 3 (blue) and 5 (red), the vertical green line shows the corresponding characteristic Ks* magnitude.