g – i colour of the cluster LSBGs (black points) and r_1/2 as a function of the projected distance from their cluster centre (in units of the cluster radius R₂₀₀); left and right panels, respectively. The UDGs are marked as red hollow circles. The green line and the grey-shaded region are the linear best fit and the 1σ scatter for the cluster LSBGs, respectively. The blue dashed line is the linear best fit for the cluster UDGs.