Why does overriding ApplicationPageBackgroundThemeBrush not work? - xaml

Question

I am trying to define a default background colour for my Windows 8 Store application, but although it shows correctly in the XAML editor and in Blend, it comes up with the default black background when run on Windows 8 and in the Windows RT emulator.
I created a brand new Windows 8 app based on the "Split App" VS 2012 template and modified App.xaml to specify a new value for ApplicationPageBackgroundThemeBrush.
This is what my App.xaml looks like:
<Application
x:Class="App3.App"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="using:App3"
xmlns:localData="using:App3.Data">
<Application.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<!--
Styles that define common aspects of the platform look and feel
Required by Visual Studio project and item templates
-->
<ResourceDictionary Source="Common/StandardStyles.xaml"/>
</ResourceDictionary.MergedDictionaries>
<!-- Application-specific resources -->
<x:String x:Key="AppName">App3</x:String>
<!-- Basic foreground and background colours -->
<SolidColorBrush x:Key="ApplicationPageBackgroundThemeBrush" Color="#FF3CA5DC"/>
<SolidColorBrush x:Key="ApplicationPageForegroundThemeBrush" Color="White"/>
</ResourceDictionary>
</Application.Resources>

Answer 1

It seems that those 2 brushes are only used by a few styles in StandardStyles.xaml, one of them is
<Style x:Key="LayoutRootStyle" TargetType="Panel">
which you can apply to your root panel. But your changes in the App.xaml doesn't affect this style. It affects only further use of this brush, so if you want to use those particular brushes I see the following variants:
1) Declare them in your App.xml and use it further like:
<Grid Background="{StaticResource ApplicationPageBackgroundThemeBrush}">
2) Declare them in StadardStyles.xaml under
<ResourceDictionary.ThemeDictionaries>
<ResourceDictionary x:Key="Default">
<!-- Style Goes Here -->
</ResourceDictionary>
</ResourceDictionary.ThemeDictionaries>
In this case all StandardStyles will be affected, but you should use LayoutRootStyle in your Grid also.
But really, using those brushes show so litle profit that I think it is better just set your panel background to what you need.