Comparison of the CMDs of the GCs NGC 6528 and NGC 6553. The left and middle panels show the CMDs of NGC 6528 (red) and NGC 6553 (blue), respectively, with their corresponding fiducial lines overplotted in white. The right panel directly compares the fiducial lines of both clusters; NGC 6528 is shown as a red solid line and NGC 6553 as a blue dashed line. The similarity between the fiducial lines highlights the close resemblance of the stellar populations.