In the ClarisImpact Calendar, "Adjacent Days" are those days which are a part of the calendar grid, but not part of the calendar month. These might be the last few days of the previous month, or the first few days of the next month, which appear at the beginning and end of a calendar created for the current month.
However, if you choose Adjacent Days in the Calendar Settings dialog after applying an Element Style, ClarisImpact will apply that Element Style to the Adjacent Days in the current calendar.
To see it happen:
1) Apply an element style to a day in the calendar.
2) Go to Calendar Settings and turn on Adjacent Days.
You will not see the problem if Adjacent Days is already checked when you apply the Element Style to a Calendar day or if you have not applied an Element Style before you check Adjacent Days.
To fix the problem, shift-click on the Adjacent Days to select them, then apply the desired Element Style from the Element Styles floater to change them back to their original appearance.