Optimised colour selection in the (I_E − H_E) vs. H_E colour-magnitude plane for EL-COSMOS and Flagship2. The blue dashed lines correspond to the non-target distribution and the solid red lines to the target distribution. The contours contain 99%, 50%, and 25% of the samples. The dotted black segments represent an optimised colour cut in this plane corresponding to a recall value of ∼95%.