如何在运行时更改资源字典颜色

In XAML:

<ResourceDictionary>
    <Color x:Key="BrushColor1">Red</Color>
    <Color x:Key="BrushColor2">Black</Color>

    <LinearGradientBrush x:Key="GradientBrush1" StartPoint="0,0.5" EndPoint="1,0.5">
        <GradientStop Color="{DynamicResource BrushColor2}" Offset="0" />
        <GradientStop Color="{DynamicResource BrushColor1}" Offset="1" />
    </LinearGradientBrush>
</ResourceDictionary>
<ResourceDictionary>
    <Color x:Ke