how to change the background colour in excel report

public DataTable ConvertArraylistToDataSet(ArrayList arrayList)
   {

       DataTable dtEntityReturned = new DataTable();

       dtEntityReturned.Columns.Add("UserID", System.Type.GetType("System.String"));
       dtEntityReturned.Columns.Add("ScheduleDate", System.Type.GetType("System.String"));
       dtEntityReturned.Columns.Add("ShiftStartTime", System.Type.GetType("System.String"));
       dtEntityReturned.Columns.Add("ShiftEndTime", System.Type.GetType("System.String"));
       dtEntityReturned.Columns.Add("Creation_Date", System.Type.GetType("System.String"));
       dtEntityReturned.Columns.Add("Cab_Pick", System.Type.GetType("System.String"));
       dtEntityReturned.Columns.Add("Cab_Drop", System.Type.GetType("System.String"));
       dtEntityReturned.Columns.Add("IsWeekend", System.Type.GetType("System.String"));
       dtEntityReturned.Columns.Add("IsClientHoliday", System.Type.GetType("System.String"));
       dtEntityReturned.Columns.Add("Remarks", System.Type.GetType("System.String"));
       dtEntityReturned.Columns.Add("Shift_Type", System.Type.GetType("System.String"));


       foreach (TMS.API.Schedule.VO_Schedule_SR objreqSR in arrayList)
       {
           DataRow myRow = dtEntityReturned.NewRow();

           myRow["UserID"] = objreqSR.UserID;
           myRow["ScheduleDate"] = objreqSR.ScheduleDate;
           myRow["ShiftStartTime"] = objreqSR.ShiftStartTime;
           myRow["ScheduleDate"] = objreqSR.ScheduleDate;
           myRow["Creation_Date"] = objreqSR.Creation_Date;
           myRow["Cab_Pick"] = objreqSR.Cab_Pick;
           myRow["Cab_Drop"] = objreqSR.Cab_Drop;
           myRow["IsWeekend"] = objreqSR.IsWeekend;
           myRow["Remarks"] = objreqSR.Remarks;
           myRow["Shift_Type"] = objreqSR.Shift_Type;


           dtEntityReturned.Rows.Add(myRow);
       }
       return dtEntityReturned;
   }

    protected void ExportToExcel_Click(object sender, EventArgs e)
    {

        TMS.API.Schedule.VO_Schedule_SC obj_Schedule = new TMS.API.Schedule.VO_Schedule_SC();
        obj_Schedule.StartDate = DateTime.Parse(txt_From_date.Text).ToString("MM/dd/yyyy HH:mm:ss");
        obj_Schedule.EndDate = DateTime.Parse(txt_To_date.Text).ToString("MM/dd/yyyy HH:mm:ss");
        obj_Schedule.Hub_ID = ddl_Hub.SelectedValue;
        obj_Schedule.UserID = string.IsNullOrEmpty(txtEmployeeID.Text) ? string.Empty : txtEmployeeID.Text;
        obj_Schedule.fullrecords="1";
        INT_Schedule obj_Int_Schedule = new INT_Schedule();
        ArrayList dsRecords = obj_Int_Schedule.GetAllImportedUser_Records(obj_Schedule, PageToDisplay, PageSize);
        DataTable dsEntityReturned = ConvertArraylistToDataSet(dsRecords);
        DataSet ds =new DataSet();
        
          if (isExecuteReportGeneration(dsEntityReturned))
            {

                string attachment = "attachment; filename=Importeduserschedule.xls";
                Response.ClearContent();
                Response.AddHeader("content-disposition", attachment);
                Response.ContentType = "application/vnd.ms-excel";

                DataTable dt = null;
                dt = dsEntityReturned;
                string tab = "";
                
                foreach (DataColumn dc in dt.Columns)
                {

                    Response.Write(tab + dc.ColumnName);

                     tab = "\t";
                }
                Response.Write("\n");


                

                int i;
                foreach (DataRow dr in dt.Rows)
                {
                    tab = "";
                    for (i = 0; i < dt.Columns.Count; i++)
                    {
                        Response.Write(tab + dr[i].ToString());
                        tab = "\t";
                    }
                    Response.Write("\n");
                }

                //HttpContext.Current.ApplicationInstance.CompleteRequest();
                Response.End();
            }

            else
            {
                ShowMessageBox("No Record(s) Found.");
            }



        }

protected bool isExecuteReportGeneration( DataTable dsResult)
    {
        bool result = true;
        try
        {


            if (dsResult == null)
            {
                result = false;
            }

            if (dsResult.Rows.Count == 0)
            {
                result = false;
            }

        }

        catch (Exception ex)
        {
            throw ex;
        }
        finally
        {
        }
        return result;

    }