Overriding application wide style - wpf

Question

I want to define a global style for textblock in the application but I also want to be able to override this default style. I always thought that the local override of style has more priority than the global one but it doesn't seems to be the case?
In the following example, the Button with content "Test" will have a "Red" foreground when I expect it to be "Aqua". If I remove the global style in Application.Resources, than it will works. Did I'm missing something?
App.xaml
<Application x:Class="ContextMenuTest.App"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
StartupUri="MainWindow.xaml">
<Application.Resources>
<Style TargetType="{x:Type TextBlock}">
<Setter Property="Foreground" Value="Red" />
</Style>
</Application.Resources>
MainWindow.xaml
<Window x:Class="ContextMenuTest.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="MainWindow" Height="350" Width="525">
<Window.Resources>
<Style TargetType="{x:Type MenuItem}" x:Key="DefaultMenuItemStyle">
<Setter Property="Foreground" Value="DarkGreen" />
</Style>
<Style TargetType="{x:Type Button}" x:Key="DefaultButtonStyle">
<Setter Property="Foreground" Value="DarkGreen" />
</Style>
</Window.Resources>
<Grid Background="Black">
<Grid.ContextMenu>
<ContextMenu>
<MenuItem Header="Menu 1" Style="{StaticResource DefaultMenuItemStyle}" />
<MenuItem Header="Menu 2" Style="{StaticResource DefaultMenuItemStyle}" />
<MenuItem Header="Menu 3" Style="{StaticResource DefaultMenuItemStyle}" />
<MenuItem Header="Menu 4" Style="{StaticResource DefaultMenuItemStyle}" />
<MenuItem Header="Menu 5" Style="{StaticResource DefaultMenuItemStyle}" />
</ContextMenu>
</Grid.ContextMenu>
<Button Content="Test" Style="{StaticResource DefaultButtonStyle}" Foreground="Aqua" />
</Grid>

Answer 1

Implicit TextBlock defined in App.xaml will not be overrided by other TextBlock styles. It's therefore recommended that you move your default TextBlock style to for example <Window.Resources>.
Please refer to the following links for more information about this.
Implicit styles in Application.Resources vs Window.Resources?
Over ride the Property setting in App.xaml: https://social.msdn.microsoft.com/Forums/vstudio/en-US/f6822a5e-09c7-489b-b85d-833f1f9356dc/over-ride-the-property-setting-in-appxaml?forum=wpf
Or simply don't define any implicit TextBlock style. Define a default Style for each Control instead.

Answer 2

Your problem is in defining your application level resources for the TextBlock instead of the Button. Most of WPF controls use TextBlocks as default way to display text content, so by trying to override your Button Foreground, you are doing it, but then it gets overriden again by TextBlock default style.
Change your App.xaml to this and you will get the result you wanted to achieve:
<Application.Resources>
<Style TargetType="{x:Type Button}">
<Setter Property="Foreground" Value="Red" />
</Style>
</Application.Resources>