Setting DataGridCell style trigger property not responding

Question

I have a DataGrid with the Foreground initialized on white, like so:

<DataGridTextColumn Header="February"
                    Binding="{Binding Path=Element[February].Value}" 
                    Width="*" 
                    Foreground="White" />

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.

<DataGrid.CellStyle>
    <Style TargetType="DataGridCell">
        <Style.Triggers>
            <Trigger Property="IsMouseOver" Value="True">
                <Setter Property="Foreground" Value="White"/>
                <Setter Property="Background" Value="Black"/>
            </Trigger>
        </Style.Triggers>
    </Style>
</DataGrid.CellStyle>

EDIT: Full code

<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
        ">
    <Grid>
        <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">

            <DataGrid.Columns>
                <DataGridTextColumn Header="Oct." Binding="{Binding Path=Element[October].Value}" Width="*" Foreground="Black"/>
                <DataGridTextColumn Header="Nov." Binding="{Binding Path=Element[November].Value}" Width="*" Foreground="White"/>
                <DataGridTextColumn Header="Dec." Binding="{Binding Path=Element[December].Value}" Width="*" Foreground="White"/>
                <DataGridTextColumn Header="Jan." Binding="{Binding Path=Element[January].Value}" Width="*" Foreground="White"/>
                <DataGridTextColumn Header="Feb." Binding="{Binding Path=Element[February].Value}" Width="*" Foreground="Black"/>
                <DataGridTextColumn Header="Mar." Binding="{Binding Path=Element[March].Value}" Width="*" Foreground="Black"/>
                <DataGridTextColumn Header="Apr." Binding="{Binding Path=Element[April].Value}" Width="*" Foreground="Black"/>
                <DataGridTextColumn Header="May" Binding="{Binding Path=Element[May].Value}" Width="*" Foreground="Black"/>
                <DataGridTextColumn Header="June" Binding="{Binding Path=Element[June].Value}" Width="*" Foreground="Black"/>
                <DataGridTextColumn Header="July" Binding="{Binding Path=Element[July].Value}" Width="*" Foreground="Black"/>
                <DataGridTextColumn Header="Aug." Binding="{Binding Path=Element[August].Value}" Width="*" Foreground="Black"/>
                <DataGridTextColumn Header="Sep." Binding="{Binding Path=Element[September].Value}" Width="*" Foreground="Black"/>
            </DataGrid.Columns>

            <DataGrid.RowHeaderTemplate>
                <DataTemplate>
                    <TextBlock Text="{Binding Path=DataContext.Element[Depth].Value, RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=DataGridRow}}"/>
                </DataTemplate>
            </DataGrid.RowHeaderTemplate>

        </DataGrid>
    </Grid>

    <Window.Resources>
        <Style TargetType="{x:Type DataGridCell}">
            <Setter Property="OverridesDefaultStyle" Value="True" />
            <Setter Property="Foreground" Value="Transparent" />

            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="{x:Type DataGridCell}">
                        <Border x:Name="BackgroundBorder" 
                        BorderThickness="1">

                            <ContentPresenter VerticalAlignment="Center" 
                                      Margin="4,0,6,0" />
                        </Border>

                        <ControlTemplate.Triggers>
                            <Trigger Property="IsMouseOver" Value="True">
                                <Setter Property="Foreground" Value="Black" />
                            </Trigger>
                        </ControlTemplate.Triggers>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
    </Window.Resources>
</Window>

Answer 1

Try to move the StyleTrigger in the ControlTemplate of DataGridCell type. Instead of using white Foreground color, use Transparent:

<Style TargetType="{x:Type DataGridCell}">
    <Setter Property="OverridesDefaultStyle" Value="True" />
    <Setter Property="Foreground" Value="Transparent" />

    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type DataGridCell}">
                <Border x:Name="BackgroundBorder" 
                        BorderThickness="1">

                    <ContentPresenter VerticalAlignment="Center" 
                                      Margin="4,0,6,0" />
                </Border>

                <ControlTemplate.Triggers>
                    <Trigger Property="IsMouseOver" Value="True">
                        <Setter Property="Foreground" Value="Black" />
                    </Trigger>
                </ControlTemplate.Triggers>
            </ControlTemplate>
        </Setter.Value>
    </Setter>                
</Style>

This Style can be stored separately in resources, such as:

• in Window.Resources

• in DataGrid.Style

• in App.xaml - best place to store styles

Make sure that for the control not directly set the properties that must be set in the styles following, because local values ​​have a higher priority than the setter styles. Read more here:

MSDN: Dependency Property Value Precedence

That is setting the local value like this:

<DataGridTextColumn Header="Oct." 
                    Foreground="Black" />

You "circumcise" a Trigger job and style setters.