Results from the fitted colour selections derived in Sect. 4.1, assuming the alternative magnitude and redshift selections described in Sect. 4.2. From left to right: completeness, purity, foreground failure rate, and background density as a function of z_l. The assumed z_l precision is δz_l = 10⁻³. Top panels: efficiency of the griz selection, detailed in Table A.1, applied to the B20 catalogue with (S/N)_E > 3 and i ≤ i_max (blue solid lines), to its subsample including galaxies with i < 24.4 (red dotted lines), to the case with i < 23.4 (green dash-dotted lines), and to the sample with z_g < 1.5 (orange dashed lines). Bottom panels: efficiency of the grizY_EJ_EH_E selection, detailed in Table A.2, applied to the B20 catalogue with (S/N)_E > 3 and i ≤ i_max (black solid lines), to its subsample with i < 23.4 (green dash-dotted lines), and to the subsample with (S/N)_E > 10 (magenta dashed lines).