Quick Tip: When you see both an OK button and and APPLY button in a dialog...like Visibility/Graphics Overrides...
The APPLY button "applies" the changes you made but does not close the dialog.
The OK button "applies" the change AND closes the dialog.
You do not have to click Apply AND then OK. If you are done making changes click OK. If you want to see your changes first, click APPLY.
Keep in mind if you click CANCEL after using APPLY Revit does not commit any of the changes you made. The OK button commits changes to the database.
I mention this because I see seasoned and new users doing this all the time.