我认为理想情况下您要寻找的要么是两个TextBlocks,要么OpacityMask应用于顶部的一个;
<Grid MaxWidth="100">
    <TextBlock Text="Hey check it out we can change object gradients! yay!" Foreground="Red"
               TextWrapping="Wrap" HorizontalAlignment="Center" VerticalAlignment="Center"/>
    <TextBlock Text="Hey check it out we can change object gradients! yay!" Foreground="Blue"
               TextWrapping="Wrap" HorizontalAlignment="Center" VerticalAlignment="Center">
             <TextBlock.OpacityMask>
                 <LinearGradientBrush StartPoint="0.1,0.1" EndPoint="0.75,0.75">
                  <LinearGradientBrush.GradientStops>
                    <GradientStop Offset="0.322" Color="Black"/>
                    <GradientStop Offset="0.739" Color="Transparent"/>
                  </LinearGradientBrush.GradientStops>
                </LinearGradientBrush>
            </TextBlock.OpacityMask>
    </TextBlock>               
</Grid>
或者您可以直接将 a 应用于LinearGradientBrush(Foreground或Background其他元素)本身,例如;
<Border Width="100" Height="50">
        <Border.Background>
                <LinearGradientBrush StartPoint="0.062,0.552" EndPoint="0.835,0.548">
                  <LinearGradientBrush.GradientStops>
                    <GradientStop Offset="0.5" Color="White"/>
                    <GradientStop Offset="0.5" Color="Black"/>
                  </LinearGradientBrush.GradientStops>
                </LinearGradientBrush>
            </Border.Background>
        <TextBlock Text="Hello World!" HorizontalAlignment="Center" VerticalAlignment="Center">
            <TextBlock.Foreground>
                <LinearGradientBrush StartPoint="0.1,0.1" EndPoint="0.75,0.75">
                  <LinearGradientBrush.GradientStops>
                    <GradientStop Offset="0.5" Color="Black"/>
                    <GradientStop Offset="0.5" Color="White"/>
                  </LinearGradientBrush.GradientStops>
                </LinearGradientBrush>
            </TextBlock.Foreground>
        </TextBlock>
    </Border>
或开始 80 年代风格的幻想;
<Border Width="100" Height="50">
        <Border.Background>
                <LinearGradientBrush StartPoint="0.472,0.047" EndPoint="0.47,0.942">
                  <LinearGradientBrush.GradientStops>
                    <GradientStop Offset="0.541" Color="White"/>
                    <GradientStop Offset="0.548" Color="Black"/>
                  </LinearGradientBrush.GradientStops>
                </LinearGradientBrush>
            </Border.Background>
            <TextBlock Text="Hello World!" HorizontalAlignment="Center" VerticalAlignment="Center">
                <TextBlock.Foreground>
                    <LinearGradientBrush StartPoint="0.472,0.047" EndPoint="0.47,0.942">
                      <LinearGradientBrush.GradientStops>
                        <GradientStop Offset="0.631" Color="Black"/>
                        <GradientStop Offset="0.635" Color="White"/>
                      </LinearGradientBrush.GradientStops>
                    </LinearGradientBrush>
                </TextBlock.Foreground>
            </TextBlock>
    </Border>
试一试,希望这会有所帮助。