Surface brightness and colour profiles. Top: UCD model surface brightness profiles for the generalized King models. We also show the profiles from the 10× oversampled PSFs shifted to match the respective filter at the centre. The vertical lines give the positions of the core and effective radii in the two filters. Bottom: μ_g − μ_z colour profile. The blue line represents the King model colour profile, the black dotted line the data. For comparison, we also show the colour profile from the single-component Sersic model. The shaded areas show the 1σ uncertainties from the ELLIPSE extraction and the grey shaded area shows the range we use to fit the gradient.