WPF样式：如何在触发器中更改GradientStop颜色

I have a Button Style:

我有一个按钮样式：

<Style x:Key="ButtonStyle1" TargetType="{x:Type Button}">
  <Setter Property="Template">
    <Setter.Value>
      <ControlTemplate TargetType="{x:Type Button}">
        <Grid>
          <Path x:Name="path1" ... Data="...some data...">
            <Path.Fill>
              <LinearGradientBrush EndPoint="0.5,-0.3" StartPoint="0.5,0.8">
                <GradientStop x:Name="gs1" Color="Green" Offset="0.44"/>
                <GradientStop Color="Black" Offset="0.727"/>
              </LinearGradientBrush>
            </Path.Fill>
          </Path>                            
        <ContentPresenter ...properties...   />
      </Grid>

     <ControlTemplate.Triggers>
       <Trigger Property="IsMouseOver" Value="True">
         <Setter TargetName="???" Property="Color" Value="Green"></Setter>
       </Trigger>
     </ControlTemplate.Triggers>
   </ControlTemplate>
 </Setter.Value>
<Style x:K