cell.CellStyle.FillPattern = FillPattern.SolidForeground;
  byte r = (byte)226;
  byte g = (byte)239;
  byte b = (byte)218;
  if (workbook is XSSFWorkbook)
  {
      cell.CellStyle.FillForegroundColor = 0;
      ((XSSFColor)cell.CellStyle.FillForegroundColorColor).SetRgb(new byte[] { r, g, b });
  }
  else
  {
      cell.CellStyle.FillForegroundColor = (((HSSFWorkbook)workbook).GetCustomPalette().FindSimilarColor(r, g, b)).Indexed;
  }