(U − B)_rest-mass diagram. In gray is shown the entire zCOSMOS-20k sample, in violet the morphological ETGs, in light red the red-sequence galaxies, in dark red the red UVJ galaxies, in pink the red SED galaxies, in orange the quiescent galaxies, and in yellow the red and passive ETGs. The upper plot shows the (U − B)_rest-mass diagram obtained for z ≤ 0.5, and the lower plot shows the diagram obtained for z > 0.5. The gray hatched area represents the region that falls outside the passive region of the (U − B)_rest-mass diagram, as defined in Sect. 2.2. The representative errorbar for both quantities is shown in the bottom right corner.