Specifically in the UI, activities that are past their date show as red unless their status is completed. I have a few use cases where it would be preferable for the final state of the activity to be a status like 'accepted' or 'denied'. I have not found in place where it is possible to set the status level as equal to Completed, so I am assuming that you would have to either do it with some type of extension or custom code?
The status of an Activity is where it stands on its path from creation to completion (started, in process, awaiting xyz, etc, etc, completed).
In this flow, 'accepted' and 'denied' aren't statuses, because they don't tell us what the next action is (or if there will be another action). We should think of these as outcomes. Assuming the activity is a proposal or similar, what about creating a custom field called Result or Outcome, with 'accepted' or 'denied' as the available options?