Distribution of targets in the RUBIES parent catalogue in different projections of the 3D parameter space of F150W−F444W colour, total F444W magnitude, and best-fit photometric redshift. Black, grey, and white contours enclose the 50th, 75th, and 95th percentiles of all sources in the catalogue, respectively. The colour coding shows the average weight of sources in a bin. For bins containing fewer than ten objects, we show individual data points. Weights are computed for targets according to their number density in this 3D parameter space such that the rarest sources receive the highest weight (see Sect. 2.4).