title: Setting DataGridCell style trigger property not responding
body: <p>I have a <code>DataGrid</code> with the Foreground initialized on white, like so:</p>
  
  <pre><code>&lt;DataGridTextColumn Header="February"
                      Binding="{Binding Path=Element[February].Value}" 
                      Width="*" 
                      Foreground="White" /&gt;
  </code></pre>
  
  <p>But when I try to set the foreground to black with a mouseover it's not working I don't know what I'm doing wrong and I could use some help, thank.</p>
  
  <pre><code>&lt;DataGrid.CellStyle&gt;
      &lt;Style TargetType="DataGridCell"&gt;
          &lt;Style.Triggers&gt;
              &lt;Trigger Property="IsMouseOver" Value="True"&gt;
                  &lt;Setter Property="Foreground" Value="White"/&gt;
                  &lt;Setter Property="Background" Value="Black"/&gt;
              &lt;/Trigger&gt;
          &lt;/Style.Triggers&gt;
      &lt;/Style&gt;
  &lt;/DataGrid.CellStyle&gt;
  </code></pre>
  
  <p><strong><code>EDIT: Full code</code></strong></p>
  
  <pre><code>&lt;Window x:Class="WPF_TEST.MainWindow"
          xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
          xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
          Title="MainWindow" Height="450" Width="850
          "&gt;
      &lt;Grid&gt;
          &lt;DataGrid Margin="150,50,150,50" x:Name="GridBinding" ItemsSource="{Binding Path=Elements[Month]}" Background="Transparent" RowBackground="Transparent" AutoGenerateColumns="False" AreRowDetailsFrozen="True" SelectionUnit="Cell" GridLinesVisibility="None" IsReadOnly="True"&gt;
  
              &lt;DataGrid.Columns&gt;
                  &lt;DataGridTextColumn Header="Oct." Binding="{Binding Path=Element[October].Value}" Width="*" Foreground="Black"/&gt;
                  &lt;DataGridTextColumn Header="Nov." Binding="{Binding Path=Element[November].Value}" Width="*" Foreground="White"/&gt;
                  &lt;DataGridTextColumn Header="Dec." Binding="{Binding Path=Element[December].Value}" Width="*" Foreground="White"/&gt;
                  &lt;DataGridTextColumn Header="Jan." Binding="{Binding Path=Element[January].Value}" Width="*" Foreground="White"/&gt;
                  &lt;DataGridTextColumn Header="Feb." Binding="{Binding Path=Element[February].Value}" Width="*" Foreground="Black"/&gt;
                  &lt;DataGridTextColumn Header="Mar." Binding="{Binding Path=Element[March].Value}" Width="*" Foreground="Black"/&gt;
                  &lt;DataGridTextColumn Header="Apr." Binding="{Binding Path=Element[April].Value}" Width="*" Foreground="Black"/&gt;
                  &lt;DataGridTextColumn Header="May" Binding="{Binding Path=Element[May].Value}" Width="*" Foreground="Black"/&gt;
                  &lt;DataGridTextColumn Header="June" Binding="{Binding Path=Element[June].Value}" Width="*" Foreground="Black"/&gt;
                  &lt;DataGridTextColumn Header="July" Binding="{Binding Path=Element[July].Value}" Width="*" Foreground="Black"/&gt;
                  &lt;DataGridTextColumn Header="Aug." Binding="{Binding Path=Element[August].Value}" Width="*" Foreground="Black"/&gt;
                  &lt;DataGridTextColumn Header="Sep." Binding="{Binding Path=Element[September].Value}" Width="*" Foreground="Black"/&gt;
              &lt;/DataGrid.Columns&gt;
  
              &lt;DataGrid.RowHeaderTemplate&gt;
                  &lt;DataTemplate&gt;
                      &lt;TextBlock Text="{Binding Path=DataContext.Element[Depth].Value, RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=DataGridRow}}"/&gt;
                  &lt;/DataTemplate&gt;
              &lt;/DataGrid.RowHeaderTemplate&gt;
  
          &lt;/DataGrid&gt;
      &lt;/Grid&gt;
  
      &lt;Window.Resources&gt;
          &lt;Style TargetType="{x:Type DataGridCell}"&gt;
              &lt;Setter Property="OverridesDefaultStyle" Value="True" /&gt;
              &lt;Setter Property="Foreground" Value="Transparent" /&gt;
  
              &lt;Setter Property="Template"&gt;
                  &lt;Setter.Value&gt;
                      &lt;ControlTemplate TargetType="{x:Type DataGridCell}"&gt;
                          &lt;Border x:Name="BackgroundBorder" 
                          BorderThickness="1"&gt;
  
                              &lt;ContentPresenter VerticalAlignment="Center" 
                                        Margin="4,0,6,0" /&gt;
                          &lt;/Border&gt;
  
                          &lt;ControlTemplate.Triggers&gt;
                              &lt;Trigger Property="IsMouseOver" Value="True"&gt;
                                  &lt;Setter Property="Foreground" Value="Black" /&gt;
                              &lt;/Trigger&gt;
                          &lt;/ControlTemplate.Triggers&gt;
                      &lt;/ControlTemplate&gt;
                  &lt;/Setter.Value&gt;
              &lt;/Setter&gt;
          &lt;/Style&gt;
      &lt;/Window.Resources&gt;
  &lt;/Window&gt;
  </code></pre>