Upper panels: galaxies detected in mock maps. “FIR-riser” criteria are imposed as for real HeViCS maps (S₅₀₀ > S₃₅₀ > S₂₅₀, S₂₅₀ > 13.2 mJy, S₅₀₀ > 30 mJy). Intersected area coloured in dark orange depicts recovered red sources. Light orange area represents detected contaminants. Violet area represents missed sources. Those genuinely red galaxies are present in our catalogue, but not as 500 μm-risers. Lower panels: redshift distribution of modelled galaxies. Different S₅₀₀∕S₃₅₀ colour cuts are imposed. These cuts are related to statistical properties of the confusion noise, which is the greatest contributor to colour uncertainties (see also Table 6). Left and right panels refer to S16 and B17, respectively.