Colour-colour diagrams for removing stellar contaminants. Only spectroscopic measurements with quality flags 3 or 4 (CL >95%) are shown in the figure. Upper panel: (B−z⁺⁺) vs. (z⁺⁺− [3.6]). Galaxies detected in the B band are shown with filled circles coloured from red to yellow according to their z_spec. Lower panel: (H−K_s) versus (K_s− [4.5]). Circles with red-to-yellow colours are B drop-outs, while grey circles are the remaining spectroscopic galaxies at z ≲ 3. In both panels, solid lines delimit the conservative boundaries we chose for the stellar locus. These are described by the following equations: (z⁺⁺− [3.6] ) < 0.5(B−z⁺⁺)−1 in the upper panel, and (K_s− [3.6] ) < (H−K_s) ∧ (H−K_s) < 0.03 in the lower panel. Stars spectroscopically confirmed are plotted with cyan symbols. Typical photometric errors are ≲0.05 mag for object with [3.6] < 24, and increase up to 0.08−0.12 mag for fainter ones.