Luminosity function of GC candidates. Top row: For blue GC candidates (0.30 < g − r ≤ 0.45 mag) from the gr-matched catalogue in the elliptical over-density region (black dashed histogram in the left panel), annular and random backgrounds (red and green dashed histograms, respectively, in the middle panel) and residuals obtained after background subtractions (red and green solid histograms in the right panel). Middle and Bottom rows: Same as top row, but for intermediate GC candidates (0.45 < g − r ≤ 0.85 mag) and red GC candidates (0.85 < g − r ≤ 1.10 mag), respectively (see Sect. 6.4).