Rest-frame UVJ colour–colour diagram. The dashed lines separate passive galaxies from star-forming ones (Williams et al. 2009). Our ALMA sample is in green. The black crosses mark the galaxies with CO upper limits. The squares with the pink borders are for our low-μ_H2 galaxies (see Sect. 4.1). The grey points are the photometric redshift members with a K-band detection. The small black dots are the spectroscopic redshift galaxies, within 3 × σ_cl of the cluster redshift, and also with a K-band detection.