r−W1 vs. g−r colour–colour plot of the four defined Fisher discriminants. For each selection, crosses represent photometric objects in the eboss6-7 area passing all the cuts in Table 2, except the cut on the Fisher discriminant. Filled dots represent those passing the cut on the Fisher disriminant with the colour coding z_spec when observed with the eboss6-7 test plates (grey colour when no reliable z_spec could be estimated from the spectrum or if the object has not been observed). For clarity, we display only one out of ten objects.