WPF Control Background - xaml

Question

My WPF control background color is not working in my Universal Windows app. Here is the xaml. The Grid background is working fine, for both grids. The content TextBlocks in the ItemsControl do appear. What am I missing?
<Page
x:Class="Jockusch.Calculator.WindowsStore.MainPage"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="using:Jockusch.Calculator.WindowsStore"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:system="using:System"
mc:Ignorable="d">
<Page.TopAppBar>
<CommandBar x:Name="TabBar" IsOpen="True" IsSticky="True">
<CommandBar.PrimaryCommands>
<AppBarButton Margin="100,0,0,0" HorizontalAlignment="Left" HorizontalContentAlignment="Right" IsEnabled="True" Name="btnNext" Icon="Next" x:Uid="AppBarNext" Label="Next1"></AppBarButton>
</CommandBar.PrimaryCommands>
</CommandBar>
</Page.TopAppBar>
<Grid Background="Yellow">
<Grid.Resources>
<Style TargetType="ItemsControl">
<Setter Property="Background" Value="Wheat">
</Setter>
</Style>
</Grid.Resources>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="299" />
<ColumnDefinition Width="100"/>
<ColumnDefinition Width="366"/>
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="200"/>
</Grid.RowDefinitions>
<local:WindowsAdAndContentWrapperView Background="Orange" Grid.Row="0" Grid.Column="0" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" x:Name="ContentView"></local:WindowsAdAndContentWrapperView>
<Grid Background="Brown" Grid.Row="0" Grid.Column="1"/>
<ItemsControl Grid.Row="0" Grid.Column="2">
<ItemsControl.Items>
<TextBlock Text="Hello"></TextBlock>
<TextBlock Text="Where are my colors?"/>
</ItemsControl.Items>
</ItemsControl>
</Grid>
</Page>