New Post: Background fill for empty cells within the table

It's doing exactly what you're telling it to do: from the workbook give me the worksheet, then the columns used (have values), of those give me the cells that are being used (have values) then set the background color.

There are many ways to accomplish it but I'd probably do:

worksheet.RangeUsed().Style.Fill.BackgroundColor = XLColor.FromArgb(1);

You can also do:

cell.Style...
range.Style...
table.Style...
worksheet.Style...
row.Style...
column.Style...