Debrief contains an unending list of undoable operations which are only cleared when the current session is closed. Most changes to the Debrief plot are undoable, whether they be creating a new feature, changing an attribute of a feature (such as color), changing the current perspective, etc. If something doesn't undo, then the changes are it's something we've overlooked, so please let us know about it using the procedure in Section 14.5.1, “Reporting bugs” and we'll correct it as soon as possible.
Each open Debrief plot has its own undo buffer, so if the undo button is disabled on a particular plot you must first make sure it's active (single click on it to do that). Furthermore, even though you may have made the edit via the Outline View, you must still click on the plot before conducting an undo operation.