更新MediaPlayerElement周围的背景颜色

Question

我在MediaPlayerElement中有一个Grid，我想在调整窗口大小时将黑色背景更改为白色。我水平拉伸了MPE，所以我想更新组件颜色，而不是网格颜色。

我该怎么做？我试图更新MPE样式没有成功...

<Page x:Class="ToDelete.MainPage"
      xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
      xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
      xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
      xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
      mc:Ignorable="d"
      Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">

      <Page.Resources>
            <Style x:Key="MediaPlayerElementStyle1" TargetType="MediaPlayerElement">
               <Setter Property="HorizontalAlignment" Value="Stretch"/>
               <Setter Property="VerticalAlignment" Value="Stretch"/>
               <Setter Property="IsTabStop" Value="False"/>
               <Setter Property="Template">
                 <Setter.Value>
                   <ControlTemplate TargetType="MediaPlayerElement">
                        <Grid x:Name="LayoutRoot">
                             <Border Background="Transparent"/>
                             <Image x:Name="PosterImage" Stretch="{TemplateBinding Stretch}" Source="{TemplateBinding PosterSource}" Visibility="Collapsed"/>
                             <MediaPlayerPresenter x:Name="MediaPlayerPresenter" IsFullWindow="{TemplateBinding IsFullWindow}" MediaPlayer="{TemplateBinding MediaPlayer}"  Stretch="{TemplateBinding Stretch}"/>
                             <ContentPresenter x:Name="TransportControlsPresenter" Visibility="{TemplateBinding AreTransportControlsEnabled}" />
                             <Grid x:Name="TimedTextSourcePresenter"/>
                        </Grid>
                   </ControlTemplate>
                 </Setter.Value>
               </Setter>
              </Style>

      </Page.Resources>

      <Grid Background="White">

            <MediaPlayerElement x:Name="mpe" 
                    Style="{StaticResource MediaPlayerElementStyle1}" 
                    Source="ms-appx:///Assets/nyancat.mp4"
                    AreTransportControlsEnabled="False" 
                    HorizontalAlignment="Stretch"  />

      </Grid>
  </Page>