Distribution in the (r − i) vs. (u − g) plane of i_AB< 22.5 galaxies with known redshift from the VVDS-Deep survey, showing the kind of selection applied to construct the VIPERS target sample. The colour selection of Eq. (9) is described by the continuous line, which empirically splits the sample into z> 0.5 (red filled circles) and z< 0.5 (blue open circles) by optimising the completeness and contamination of the high-redshift sample.