Distribution of RUBIES targets for the PRISM (top) and G395M (bottom) observations in the colour-colour space of the NIRCam broad filters F115W−F200W and F277W−F444W. The symbols and colour scale are the same as in Fig. 4. We only show targets with z_phot>3 and F444W<26.5. Although RUBIES targets were not selected in this parameter space, the RUBIES selection function samples the (broad) distribution very well. The completeness fraction increases along both colour axes and reaches very high values (>80%) in the extremes.