Sub DDOnExit()
ActiveDocument.Unprotect
   Select Case ActiveDocument.FormFields("Dropdown1").Result
     Case "Positive": Selection.Tables(1).Columns(Selection.Cells(1).ColumnIndex).Shading.BackgroundPatternColorIndex = wdBrightGreen
        Case "Negative": Selection.Tables(1).Columns(Selection.Cells(1).ColumnIndex).Shading.BackgroundPatternColorIndex = wdDarkRed
  End Select
  ActiveDocument.Protect wdAllowOnlyFormFields, True
End Sub