CS0104: Color is an ambiguous reference between System.Drawing.Color and iTextSharp.text.Color

Plz solve this error.

 Code

using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Data.SqlClient;
using System.Drawing;
using System.IO;
using iTextSharp.text;
using iTextSharp.text.pdf;
using iTextSharp.text.html.simpleparser;
 
public partial class Server_Admin_Printresult : System.Web.UI.Page
{
    //server=204.93.174.60;user id=aster_medical2013;password=jagannath78;database=aster_rxexperience
    SqlConnection con = new SqlConnection("Data Source=STAR-PC;Initial Catalog=nursingboard;Integrated Security=True");
    DataTable dt = new DataTable();
     
    protected void Page_Load(object sender, EventArgs e)
    {
        if (Session["Table"] != null)
        {
 
            DataTable dt = (DataTable)Session["Table"];
            GridView1.DataSource = dt;
            GridView1.DataBind();
            HighlightDuplicate(this.GridView1);
            
        }
    }
    public void HighlightDuplicate(GridView grv)
    {
        //use the currentRow to compare against
        for (int currentRow = 0; currentRow < grv.Rows.Count - 1; currentRow++)
        {
            GridViewRow rowToCompare = grv.Rows[currentRow];
            //specify otherRow as currentRow + 1
            for (int otherRow = currentRow + 1; otherRow < grv.Rows.Count; otherRow++)
            {
                GridViewRow row = grv.Rows[otherRow];
 
                bool duplicateRow = true;
                //compare cell rollno between the two rows
                if (rowToCompare.Cells[2].Text != row.Cells[2].Text)
                {
                    duplicateRow = false;
                    //break;
                }
                //highlight both the currentRow and otherRow if rollno matches
                if (duplicateRow)
                {
                    rowToCompare.BackColor = Color.Red;
                    rowToCompare.ForeColor = Color.Black;
                    row.BackColor = Color.Red;
                    row.ForeColor = Color.Black;
                    //Button1.Visible = false;
                }
                else
                {
                 
                }
            }
        }
    }
 
 
 
 
    protected void Button1_Click(object sender, EventArgs e)
    {
        Response.ClearContent();
        Response.Buffer = true;
        Response.AddHeader("content-disposition", string.Format("attachment; filename={0}", "duplicatereport.xls"));
        Response.ContentType = "application/ms-excel";
        StringWriter sw = new StringWriter();
        HtmlTextWriter htw = new HtmlTextWriter(sw);
        GridView1.AllowPaging = false;
        //Change the Header Row back to white color
        GridView1.HeaderRow.Style.Add("background-color", "#FFFFFF");
        //Applying stlye to gridview header cells
        for (int i = 0; i < GridView1.HeaderRow.Cells.Count; i++)
        {
            GridView1.HeaderRow.Cells[i].Style.Add("background-color", "#507CD1");
        }
        int j = 1;
        //This loop is used to apply stlye to cells based on particular row
        foreach (GridViewRow gvrow in GridView1.Rows)
        {
 
            if (j <= GridView1.Rows.Count)
            {
                if (j % 2 != 0)
                {
                    for (int k = 0; k < gvrow.Cells.Count; k++)
                    {
                        gvrow.Cells[k].Style.Add("background-color", "#EFF3FB");
                    }
                }
            }
            j++;
        }
        GridView1.RenderControl(htw);
        Response.Write(sw.ToString());
        Response.End();
    }
    public override void VerifyRenderingInServerForm(Control control)
    {
        /* Verifies that the control is rendered */
    }
    protected void Button2_Click(object sender, EventArgs e)
    {
        Response.ContentType = "application/pdf";
        Response.AddHeader("content-disposition", "attachment;filename=Duplicaterecord.pdf");
        Response.Cache.SetCacheability(HttpCacheability.NoCache);
        StringWriter sw = new StringWriter();
        HtmlTextWriter hw = new HtmlTextWriter(sw);
        GridView1.AllowPaging = false;
        GridView1.DataBind();
        GridView1.RenderControl(hw);
        GridView1.HeaderRow.Style.Add("width", "15%");
        GridView1.HeaderRow.Style.Add("font-size", "10pt");
        GridView1.Style.Add("text-decoration", "none");
        GridView1.Style.Add("font-family", "Arial, Helvetica, sans-serif;");
        GridView1.Style.Add("font-size", "8pt");
        StringReader sr = new StringReader(sw.ToString());
        Document pdfDoc = new Document(PageSize.A2, 7f, 7f, 7f, 0f);
        HTMLWorker htmlparser = new HTMLWorker(pdfDoc);
        PdfWriter.GetInstance(pdfDoc, Response.OutputStream);
        pdfDoc.Open();
        htmlparser.Parse(sr);
        pdfDoc.Close();
        Response.Write(pdfDoc);
        Response.End();
 
    }
}