Default TextBlock style overriding button text color

See answer 5 at this link

This happends because the ContentPresenter creates a TextBlock for a string content, and since that TextBlock isn't in the visual tree, it will lookup to Application level resource. And if you define a style for the TextBlock at Application level, then it will be applied to these TextBlock within ContentControl

A workaround is to define a DataTemplate for System.String, where we can explicitly use a default TextBlock to display the content. You can place that DataTemplate in the same dictionary you define the TextBlock style so that this DataTemplate will be applied to whatever ContentPresenter effected by your style.

Try adding this to the ResourceDictionary

<DataTemplate DataType="{x:Type sys:String}">
    <TextBlock Text="{Binding}">
        <TextBlock.Resources> 
            <Style TargetType="{x:Type TextBlock}"/>
        </TextBlock.Resources>
    </TextBlock>
</DataTemplate>

You are better off not overriding default style for the TextBlock. The best idea I could come up with so far is to create a style for Control and apply it to all top level windows.

<!-- App.xaml -->
<Application.Resources>
    <Style x:Key="RedStyle" TargetType="{x:Type Control}">
        <Setter Property="TextTrimming" Value="CharacterEllipsis"/>
        <Setter Property="Foreground" Value="Red"/>
    </Style>
</Application.Resources>

<!-- MainWindow.xaml -->
<Window Style="{StaticResource RedStyle}" ...>
    ...
</Window>

See here for more details: http://www.ikriv.com/dev/dotnet/wpftextstyle/