Hi:
This isn't really a question for the SAS/GRAPH and ODS Graphics forum. This would be better addressed in the ODS and Reporting forum.
However, when you change a style template and you want to turn off a style attribute value, you generally use the _UNDEF_ value for the style attribute.
I'm not sure that Document is the right style element to change, however. If you look at this paper on customizing a style template for use with TAGSETS.EXCELXP, you might find some pointers that will help you.
http://www2.sas.com/proceedings/forum2008/036-2008.pdf
I'm not sure, also, what you mean by "Excel has a default background fill color of white." Generally, the way that your output is defined in the TAGSETS.EXCELXP XML is for the interior table lines to show only around the data cells in the tabular output created by SAS. so, for example, if I use PROC PRINT on SASHELP.CLASS, I see interior table lines around OBS, NAME, SEX, AGE, HEIGHT and WEIGHT variables for 19 rows, plus a header row, but I do not see interior lines in any of the rest of the worksheet. I believe this behavior is working as designed. You might want to check with Tech Support.
I know that there is a GRIDLINES sub-option which turns on the printing of GRIDLINES for the print area. But I don't think this is what you mean.
cynthia