Distribution of galaxies, stars, and QSOs in the (z−K) vs. (g−z) colour diagram. Density levels are in logarithmic scale (Δ = 0.3 dex) for galaxies (solid lines in W1 and W4 fields shown blue and red, respectively) and stars (dashed lines in green and orange). Objects from our QSO samples are shown as open stars (blue: W1; red: W4), while the SDSS/VIPERS AGN sample is shown as orange dots. The solid black lines delineate the high-redshift BzK populations (star-forming and passive galaxies).