Optical g − r versus r − z colour-colour distribution of cluster galaxies. Grey points are potential cluster members selected via the J − K versus K CM relation, filtered further by photometric redshift (0.29 ≤ z_phot ≤ 0.49). This galaxy colour separation shows its evolution from star-forming to being quenched and behaves as a proxy to photometrically separate them. Red circles denote quenched galaxies and blue stars are star-forming ones and have IMACS spectroscopy. Black dashed lines separate these two types, with quenched galaxies concentrated in a clump above and star-forming galaxies spread below.