There are a few ways to calibrate your Monitor, first is using the monitor controls/software/apples calibration assistant or you can purchase a calibration kit, there are a few available, but ive found 2 that are exceptionally good, either Colorvision spyder or Pantone Huey personally I use the colorvision spyder and i'm happy with that, no problems at all using it with 10.5.2, There are plenty of sites if you google the subject offering advice, happy hunting 😉