When I apply a background color to a group of cells, then later remove the
background color, the cells' gridlines (or borders) disappear. The rest of
the spreadsheet has the default gridlines; applying a border of any kind
(through Format|Cells|Border) does not match the rest of the cells. How do I
get the default border back around the "un-bordered" cells, so that it looks
as though a background color was never applied?