title: Whats wrong with this trigger?
body: <p>I'm learning about WPF templates and I'm creating one for a button.  I'm using a trigger to change the Fill property of the Ellipse on 'IsMouseOver'.  When I set the trigger to the 'Fill' property directly, it works.  But when I try to reference a specific SolidColorBrush, I get a compile error.</p>
  
  <p>This works:</p>
  
  <pre><code>&lt;ControlTemplate x:Key="GhostButtonTemplate" TargetType="Button"&gt;
          &lt;Grid&gt;
              &lt;Ellipse Name="Border" Stroke="DarkGray" Fill="Gray"&gt;        
          &lt;/Ellipse&gt;
              &lt;ContentPresenter ... /&gt;
          &lt;/Grid&gt;
      &lt;ControlTemplate.Triggers&gt;
          &lt;Trigger Property="IsMouseOver" Value="True"&gt;
          &lt;Setter TargetName="Border" Property="Fill" Value="Black"/&gt;
          &lt;/Trigger&gt;
      &lt;/ControlTemplate.Triggers&gt;
  &lt;/ControlTemplate&gt;
  </code></pre>
  
  <p>This causes error:</p>
  
  <pre><code>&lt;ControlTemplate x:Key="GhostButtonTemplate" TargetType="Button"&gt;
          &lt;Grid&gt;
              &lt;Ellipse Name="Border" Stroke="DarkGray"&gt;
                  &lt;Ellipse.Fill&gt;
                      &lt;SolidColorBrush Color="Gray" x:Name="FillBrush"/&gt;
              &lt;/Ellipse.Fill&gt;         
          &lt;/Ellipse&gt;
              &lt;ContentPresenter ... /&gt;
          &lt;/Grid&gt;
      &lt;ControlTemplate.Triggers&gt;
          &lt;Trigger Property="IsMouseOver" Value="True"&gt;
          &lt;Setter TargetName="FillBrush" Property="Color" Value="Black"/&gt;
          &lt;/Trigger&gt;
      &lt;/ControlTemplate.Triggers&gt;
  &lt;/ControlTemplate&gt;
  </code></pre>
  
  <p>Error is: </p>
  
  <blockquote>
    <p>Cannot find the Trigger target
    'FillBrush'.  (The target must appear
    before any Setters,Triggers, or
    Conditions that use it.)</p>
  </blockquote>
  
  <p>Can anyone explain why the second case doesn't work?  Thanks.</p>