Colour–colour diagram for objects detected in the NB1060 image and brighter than NB1060(AUTO) = 24.8. The top panel represents the colour distribution of continuum and emission-line galaxies. The expected region occupied by continuum emitters is enclosed by a red dashed line, whereas the region we use to select candidate line emitters lies below the blue dotted line. Red dots represent objects from the basic sample, i.e. objects that meet the selection criteria. The lower panel additionally shows objects in green circles and green diamonds that have emission-lines but do not enter our basic sample because they either are masked or lie outside a conservatively defined selection area (therefore above the blue dotted line).