Color-color Hess diagrams of the preselected GC candidates in the ugri (left panel) and gri (right) catalogs. Solid black lines are the isodensity contours of GCs from the master catalog used in Cantiello et al. (2020). Each isodensity contour contains a certain percentage of GCs from the master catalog. In particular, going from the outer contour (lower GCs density) to the inner one (higher GCs density) the contours contain: 90%, 85%, 80%, 70%, 60%, 30%, 20%, and 10% of GCs in the master catalog. The 85% (80%) isodensity contour used for the selection are highlighted in blue (left) and magenta (right).