I am developing a windows phone app and my requirements include to use a specific color theme and not use the default theme (Light/Dark/etc.) of the phone.

I'm stuck at formatting/templating the headers of textboxes. The following code in the app.xaml is not working:

```
<DataTemplate x:Key="HeaderTemplate">
    <TextBlock Text="{Binding}" Foreground="Black"/>
</DataTemplate>

<Style TargetType="TextBox">
    <Setter Property="Foreground" Value="#FFBBB8B8"/>
    <Setter Property="BorderBrush" Value="LightGray"/>
    <Setter Property="HeaderTemplate" Value="{StaticResource HeaderTemplate}"/>
</Style>

```

Is there either a way just to configure the theme used or a way to implement the template for the headers?