Left panel: CMD of the source 3CR 089. The blue dot represents the host of 3C 089; the red dots are the spectroscopic companions identified through SDSS data; the red lines represent the boundaries of the RS from O’Mill et al. (2019); and the green dots are the sources falling inside the RS with absolute magnitude M_r < −17. Right panel: CMD of the source 3CR 063. The RS in this source is less clearly defined.