datatable中对符合要求格显示为红色

            GridView1.DataSource = dt.DefaultView;

            GridView1.DataBind();

            for (int i = 0; i < dt.Rows.Count; i++)
            {
                int a= Convert.ToInt32(dt.Rows[i][1]);
                int b = Convert.ToInt32(dt.Rows[i][3]);
                if (a < b)
                {
                    GridView1.Rows[i].Cells[3].ForeColor = System.Drawing.Color.Red;
                }
            }