Representative colour–colour plots for the galaxy training sample. Open black squares represent objects with i′-apparent magnitude between 19 and 20 mag; green X-s – galaxies with i′ magnitude between 20 and 21 mag; objects with i′ apparent magnitude between , and mag are marked as blue +-s and open red triangles, respectively; in the middle panel of colour–colour plots, the boundaries of VIPERS selection are marked as magenta lines.