Trouble formatting excel spreadsheet

Hi there I'm trying to format an excel spreadsheet using Apache 2, PHP 5 and PEAR on Windows XP. Here's the code: $workbook=new Spreadsheet_Excel_Writer("test.xls"); // Add a new worksheet $worksheet=& $workbook->addWorksheet("Electricity Transactions"); // add the color format to the workbook $format_color=& $workbook->addFormat(); $format_color->setBgColor('green'); $format_color->setPattern(0); $ReturnBalance=2; $worksheet->write(2, 1, "Current Balance : R ".number_format($ReturnBalance, 2), $format_color); $workbook->close(); But when I open the spreadsheet the background of the cell is white. What gives? Cheers Louis