Non-JIRA events can be added to calendar which can be seen only in calendar where they were created. Select one day or period you need and select "New non-JIRA event":

The event will be added to current calendar. It has only one attribute - Name, can be moved, stretched and trimmed by drag&drop and deleted permanently.

Event Set UpScreenshot
  1. Event's name.
  2. Event's background color.
  3. Event's text color.
  4. When checked the day/days of event is/are highlighted in selected event's background color, other issues and events can be placed at the selected days but the background will be coloured, not blank.

     Calendar view...