The steps are:

1.       Change the column XAML for “Trade” to use cell template:

                <data:DataGridTemplateColumn Header="Trade" Width="80">

                    <data:DataGridTemplateColumn.CellTemplate>

                        <DataTemplate>

                            <TextBlock TextAlignment="Right" VerticalAlignment="Center"  FontSize="12" Text="{Binding last}" Foreground ="{Binding lastForegroundColor}"></TextBlock>

                        </DataTemplate>

                    </data:DataGridTemplateColumn.CellTemplate>

         </data:DataGridTemplateColumn>

2.       Adding a function to determine the color of row:

        private String GetLastForegroundColor(string last, string previousClose)

        {

            if (Convert.ToDouble(last) > Convert.ToDouble(previousClose))

            {

                return "Green";

            }

            else if (Convert.ToDouble(last) < Convert.ToDouble(previousClose))

            {

                return "Red";

            }

            else

            {

                return "Black";

            }

        }

        Adding the following line into the DisplayInDataGrid function and new OneStock section.

lastForegroundColor = GetLastForegroundColor(g.Element("Last").Value, g.Element("PreviousClose").Value)

3.       Ctrl-F5 and we should see the “Trade” column show either green, red depending on the current stock price.