Colour-magnitude diagram of the detected sources (grey points) versus the spectroscopically confirmed GCs (red points) and GCs in the ACSFCS catalogue (yellow points). Considering the photometric uncertainties of the fainter GCs (fainter than I_E = 22), the majority of the known GCs have 0.0 < I_E − Y_E < 0.8, −0.3 < Y_E − J_E < 0.5, and −0.3 < J_E − H_E < 0.5. In this work, we use these colour ranges and apply a colour cut for GC selection.