Stellar mass versus spectroscopic redshift and rest-frame U−V colour estimated from eazy fitting to PSF-matched photometry of Weibel et al. (2024a) for targets with robust spectroscopic redshifts. The sources that were selected with high priority based on their F150W−F444W colour are marked in red. The RUBIES sources span a wide range in redshift, stellar mass, and rest-frame colour, with the census sample being predominantly blue and of lower stellar mass. The red sources tend to be massive (M_*≳10¹⁰ M_⊙), although there is large diversity in the rest-frame U−V colour at the highest stellar masses. We identify a redshift clustering of approximately 15 massive (M_*>10¹⁰ M_⊙) red galaxies at z_prism≈3.2, which also corresponds to a spatial clustering in the UDS field and coincides with the early massive quiescent galaxy of Glazebrook et al. (2024).