Export To Excel with Cell Formating

 using System.Text;
          using System.IO;
          using System.Drawing;
           Response.Clear();
            Response.Buffer = true;

            Response.AddHeader("content-disposition",
            "attachment;filename=GridViewExport.xls");
            Response.Charset = "";
            Response.ContentType = "application/vnd.ms-excel";
            StringWriter sw = new StringWriter();
            HtmlTextWriter hw = new HtmlTextWriter(sw);
            GridView GridView1 = new GridView();
            GridView1.DataSource = ds;
            GridView1.DataBind();
            GridView1.AllowPaging = false;
            GridView1.DataBind();
            //Change the Header Row back to white color
            GridView1.HeaderRow.Style.Add("background-color", "#FFFFFF");
            //Apply style to Individual Cells
            GridView1.HeaderRow.Style.Add("background-color", "green");
            //GridView1.HeaderRow.Cells[1].Style.Add("background-color", "green");
            //GridView1.HeaderRow.Cells[2].Style.Add("background-color", "green");
            //GridView1.HeaderRow.Cells[3].Style.Add("background-color", "green");

            for (int i = 0; i < GridView1.Rows.Count; i++)
            {
                GridViewRow row = GridView1.Rows[i];
                //Change Color back to white
                row.BackColor = System.Drawing.Color.White;
                //Apply text style to each Row
               // row.Attributes.Add("class", "textmode");

                //Apply style to Individual Cells of Alternating Row
                if (i % 2 != 0)
                {
                    row.Style.Add("background-color", "#C2D69B");
                    //row.Cells[1].Style.Add("background-color", "#C2D69B");
                }
            }
            GridView1.RenderControl(hw);
            //style to format numbers to string
            string style = @"<style> .textmode { mso-number-format:\@; } </style>";
            Response.Write(style);
            Response.Output.Write(sw.ToString());
            Response.Flush();
            Response.End();