Workbook::setCustomColor

require_once 'Spreadsheet/Excel/Writer.php';

$workbook = new Spreadsheet_Excel_Writer();
$worksheet =& $workbook->addWorksheet();

// "regular" green
$format_regular_green =& $workbook->addFormat();
$format_regular_green->setFgColor('green');

// "special" green
$format_special_green =& $workbook->addFormat();
$format_special_green->setFgColor(11);

// our green (overwriting color on index 12)
$workbook->setCustomColor(12, 10, 200, 10);
$format_our_green =& $workbook->addFormat();
$format_our_green->setFgColor(12);

$worksheet->setColumn(0, 0, 30);

$worksheet->write(0, 0, "Regular green", $format_regular_green);
$worksheet->write(1, 0, "Special green (index 11)", $format_special_green);
$worksheet->write(2, 0, "Our green", $format_our_green);

$workbook->send('greens.xls');
$workbook->close();