I have a workbook with multiple sheets. On one sheet, I have a cell where I
manually change the contents from 1 to 12 (corresponding to months of the
year). This number then is used in formulas to sum columns 1-12, depending on
what the number is I have entered.

Is there a way to format a cell, say fill the cell with a colour, above each
column that is being summed as described above so that the columns that are
not being summed have a blank cell above them?