Star-forming and quiescent galaxy selection in the NUVrK diagram. The colour code shows the galaxy density. The averaged colour uncertainties (based on the observed photometric errors) are shown in the upper left corner of each panel. The binning used for the density map is tuned to match the typical uncertainties at 0.2 <z< 0.5. The solid line represents the mean selection of quiescent galaxies in a given redshift bin. The dotted lines represent the two extreme selections delimiting the green valley.