Java Apache POI - XSSFCell setFillBackgroundColor Has No Effect

I have looked all over stack overflow and could not seem to get my java code to fill the background color of an XSSF excel cell. From what others have said, this should make the top left corner cell yellow:

// Example Code
try {

    // prepare
    FileInputStream resource = new FileInputStream( FILEPATH + FILENAME );
    XSSFWorkbook workbook = new XSSFWorkbook( resource );
    XSSFSheet sheet = workbook.createSheet( "Example Sheet" );

    // create
    XSSFRow row = sheet.createRow( 0 );
    XSSFCell cell = row.createCell( 0 );
    XSSFCellStyle style = workbook.createCellStyle();
    XSSFColor color = new XSSFColor( Color.YELLOW );

    // stylize
    style.setFillBackgroundColor( color );
    cell.setCellStyle( style );

    // finalize
    FileOutputStream output = new FileOutputStream( "Example Workbook.xlsx" );
    workbook.write( output );
    workbook.close();

} catch ( Exception e ) {

    // error
    e.printStackTrace();

}

...but it doesn't. Can someone let me know what I am doing wrong? I am using Apache POI version 3.16 by the way.

Thanks!