Color–magnitude diagram J − K_S versus K_S. The density map shows the whole sample in the central region of the cluster (color scale corresponds to the percentage of objects with respect to the total number, as shown in the key). The red-sequence model is represented by a solid line and the ± 5σ around the model by dashed lines. The dots correspond to the sources that met the selection criteria of Sect. 3.1. The crosses mark the red-sequence galaxies with visual confirmation. The red sequence, fitted to the bright galaxy cluster member candidates, is shown by the dotted line.