Test of the colour–colour redshift selection, using galaxies with known redshift from the VVDS-Deep survey, limited to i_AB< 22.5. The colour locus in Fig. 3 is used to separate a priori galaxies lying below (blue-dashed line) and above (solid red line) z ≃ 0.5. The dotted black line shows the global dN/dz of the sample. The VVDS-Deep sample has been limited to objects belonging to tile # 25 (where the bulk of the sample is concentrated), given that this has been used as the reference for the global colour calibration discussed in the text.