sSFR vs. (U − B)_rest colour for morphological ellipticals in the sample. Empty black points represent galaxies with no spectrum. Filled points indicate galaxies with a spectrum, and are colour-coded with respect to the spectral classification: red for early-types, blue for star-forming, and green for AGNs. The vertical line marks the sSFR cut to select passive galaxies. The horizontal line marks the separation between red and blue galaxies. The grey area identifies the locus in the plane where “red and passive” galaxies fall.