Left panel: (g − z) vs. (z − K) colour–colour diagram for VUDS galaxies with 1.4 < z < 2.5 (flags 3 and 4: red squares, flag 2: blue triangles). The average colour errors are indicated in the lower left corner. Galaxies in this plot are detected in all three bands at more than 3σ (95% of the sample). The gzK selection would have selected 91% of the VUDS galaxies with 1.4 < z < 2.5. Right panel: same for galaxies either with z < 1.4 (open squares) or z > 2.5 (magenta filled squares). Stars are represented by green star symbols. There is a high level of contamination as 58% of galaxies in the selection area of the gzK are outside the redshift range 1.4 < z < 2.5, coming mostly from galaxies at z > 2.5. (inset) redshift distribution of galaxies in the gzK selection area, the grey shaded histogram represents galaxies outside the redshift range 1.4 < z < 2.5.