How to chage color of cell in data grid

<Window x:Class="WpfApplication3.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Window1" Height="299" Width="503" xmlns:my="http://schemas.microsoft.com/wpf/2008/toolkit">
    <Grid>
        <my:DataGrid AutoGenerateColumns="False" Margin="10,10,61,51" Name="dataGrid1">
            <my:DataGrid.Columns>
                <my:DataGridTemplateColumn Header="Icon" Width="50" IsReadOnly="True" >
                    <my:DataGridTemplateColumn.CellTemplate>
                        <DataTemplate>
                            <Image Source="{Binding Path=ImgPath}" Width="20" Height="20"/>
                        </DataTemplate>
                    </my:DataGridTemplateColumn.CellTemplate>
                </my:DataGridTemplateColumn>
                <my:DataGridTextColumn Header="Position"  Binding="{Binding Path=PO}"   />
                <my:DataGridTextColumn Header=" Name" Binding="{Binding Path=NA}"  />
                <my:DataGridTextColumn Header="Gender" Binding="{Binding Path=GE}"  />
                <my:DataGridTemplateColumn Header="Status" Width="50" IsReadOnly="True"  >
                    <my:DataGridTemplateColumn.CellTemplate>
                        <DataTemplate>
                            <Label Name="lbl" Content="{Binding Path=ST}" Foreground="Green" />
                        </DataTemplate>
                    </my:DataGridTemplateColumn.CellTemplate>
                </my:DataGridTemplateColumn>
                <my:DataGridTextColumn Header="Machine" Binding="{Binding Path=MA}"  />
            </my:DataGrid.Columns>
        </my:DataGrid>
    </Grid>
</Window>

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using System.Data;

namespace WpfApplication3
{
    /// <summary>
    /// Interaction logic for Window1.xaml
    /// </summary>
    public partial class Window1 : Window
    {
        public DataTable dt;
        public Window1()
        {
            InitializeComponent();
            dt = new DataTable();
            dt.Columns.Add("PO");
            dt.Columns.Add("NA");
            dt.Columns.Add("GE");
            dt.Columns.Add("ST");
            dt.Columns.Add("MA");
            dt.Columns.Add("ImgPath", typeof(BitmapImage));

            DataRow dr = dt.NewRow();
            dr[0] = "1";
            dr[1] = "SAM";
            dr[2] = "Male";

            dr[3] = "Offline";
            dr[4] = "Comp123";
            dr[5] = new BitmapImage(new Uri("/WpfApplication3;component/Images/play.png", UriKind.RelativeOrAbsolute));
            dt.Rows.Add(dr);

            dr = dt.NewRow();
            dr[0] = "2";
            dr[1] = "JOY";
            dr[2] = "Male";

            dr[3] = "Online";

            dr[4] = "Comp124";
            dr[5] = new BitmapImage(new Uri("/WpfApplication3;component/Images/play.png", UriKind.RelativeOrAbsolute));
            dt.Rows.Add(dr);

            dr = dt.NewRow();
            dr[0] = "3";
            dr[1] = "ADITYA";
            dr[2] = "Male";
            dr[3] = "Online";
            dr[4] = "Comp124";
            dr[5] = new BitmapImage(new Uri("/WpfApplication3;component/Images/play.png", UriKind.RelativeOrAbsolute));
            dt.Rows.Add(dr);

            dr = dt.NewRow();
            dr[0] = "4";
            dr[1] = "VISHAL";
            dr[2] = "Male";
            dr[3] = "Offline";
            dr[4] = "Comp124";
            dr[5] = new BitmapImage(new Uri("/WpfApplication3;component/Images/play.png", UriKind.RelativeOrAbsolute));
            dt.Rows.Add(dr);

            dr = dt.NewRow();
            dr[0] = "5";
            dr[1] = "ANAY";
            dr[2] = "Male";
            dr[3] = "Online";
            dr[4] = "Comp124";
            dr[5] = new BitmapImage(new Uri("/WpfApplication3;component/Images/play.png", UriKind.RelativeOrAbsolute));
            dt.Rows.Add(dr);

            dataGrid1.ItemsSource = dt.DefaultView;
            dataGrid1.SelectedValuePath = "NA";

            DataRow[] result = dt.Select("PO >= 2");
            // AND Sex = 'm'");
            foreach (DataRow row in result)
            {

                //here i want to change the color of online from red to green please help me
            }
        }
    }
}