DataTable table = new DataTable();

//some code here
//lets say the cell is [0,0]
//change the foregroud color like this

table.columns[0].rows[0].forgroundColor ="red";

table.Columns[0].Rows[0].ForegroundColor = Color.Red;

TableItemStyle tableCellStyle = new TableItemStyle();
tableCellStyle.ForeColor=System.Drawing.Color.Red;

DataSeta.BalanceSheetRow AssetsStockRow = (DataSeta.BalanceSheetRow)BalanceSheet.NewRow();
     AssetsStockRow.CurrentAssetACC = "Stock Value";
     AssetsStockRow.CurrentAssetAmt = Common.ConvertToDouble(stockValue.ToString()).ToString("00.00");
     AssetsStockRow.style = "style="color: gray;"";
     BalanceSheet.Rows.Add(AssetsStockRow);

<Columns>
            <asp:TemplateField HeaderText="Sl. No.">
                <ItemTemplate>
                    <%# Container.DataItemIndex + 1 %>
                </ItemTemplate>
            </asp:TemplateField>

            <asp:TemplateField HeaderText="Current Assests" ItemStyle-HorizontalAlign="Right">
                <ItemTemplate>
                    <div <%#Eval("style") %>><%#Eval("CurrentAssetACC") %></div>
                </ItemTemplate>
            </asp:TemplateField>
        </Columns>