FileStream fs = new FileStream(ExcelPath, FileMode.Open);
             HSSFWorkbook workbook = new HSSFWorkbook(fs);
             HSSFSheet currentSheet = (HSSFSheet)workbook.GetSheet("sheet");
             HSSFCellStyle style8 = (HSSFCellStyle) workbook.CreateCellStyle();
             style8.FillForegroundColor = NPOI.HSSF.Util.HSSFColor.WHITE.index;
         
             style8.FillBackgroundColor = NPOI.HSSF.Util.HSSFColor.RED.index;
             HSSFCell cell = new HSSFCell(workbook, currentSheet, 4, (short)(4));
             cell.CellStyle = style8;
             cell.SetCellValue("123");
fs.close();