error in code............

protected void CalendarDRender(object sender, System.Web.UI.WebControls.DayRenderEventArgs e)
    {
        // If the month is CurrentMonth
        if (!e.Day.IsOtherMonth)
        {
            foreach (DataRow dr in ds.Tables[0].Rows)
            {
                if ((dr["EventDate"].ToString() != DBNull.Value.ToString()))
                {
                    DateTime dtEvent = (DateTime)dr["EventDate"];
                    if (dtEvent.Equals(e.Day.Date))
                    {
                        e.Cell.BackColor=Colors.Red;//Colors does not exist in the current context i develop calender and on which date i set event color of that date change
                    }
                }
            }
        }
        //If the month is not CurrentMonth then hide the Dates
        else
        {
            e.Cell.Text = "";
        }
    }