NPOI Excel同一个单元格 多种字体

public static void CreateFont()
{
    IWorkbook workbook = new HSSFWorkbook();
    workbook.CreateSheet("sheet1");
    using (FileStream fs = File.Create("D:\1.xls"))
    {
        IFont font1 = workbook.CreateFont();
        font1.FontName = "楷体";
        font1.Color = HSSFColor.Red.Index;
        font1.Boldweight = (short)FontBoldWeight.Normal;

        IFont font2 = workbook.CreateFont();
        font2.FontName = "楷体";
        font2.Color = HSSFColor.Blue.Index;
        font2.Boldweight = (short)FontBoldWeight.Normal;

        var rts1 = new HSSFRichTextString("百事可乐®");
        rts1.ApplyFont(0, 2, font1);
        rts1.ApplyFont(2, 4, font2);
        ISheet sheet = workbook.GetSheetAt(0);
        var _icell = sheet.CreateRow(1).CreateCell(0);
        _icell.SetCellValue(rts1);
        workbook.Write(fs);
    }
}