title: wpf comboBox coloring issue
body: <p>Due to requirements, I need to have a comboBox that works as follows:</p>
  
  <p>It uses:
   - one set of colors for fore/background when in view mode
   - A second set of colors for fore/background when in edit mode
   - Another set for selected mode (when the cursor is in the comboBox)
   - Another set for disabled mode</p>
  
  <p>The user will never be able to edit the contents, just click on the down arrow and select from the list.</p>
  
  <p>I have the comboBox working except for the colors.  Unlike other controls, simply trying to do the following (the triggers for edit mode) just doesn't work:</p>
  
  <pre><code>&lt;MultiTrigger&gt;
  &lt;MultiTrigger.Conditions&gt;
      &lt;Condition Property="IsFocused"
           Value="false" /&gt;
      &lt;Condition Property="wpfMisc:myCtrl.viewMode"
           Value="false" /&gt;
      &lt;Condition Property="IsEnabled"
           Value="true" /&gt;
  &lt;/MultiTrigger.Conditions&gt;
  &lt;Setter Property="BorderBrush"
      Value="{DynamicResource controls-editableBorderBrush}" /&gt;
  &lt;Setter Property="Background"
      Value="{DynamicResource controls-editableBackgroundBrush}" /&gt;
  &lt;Setter Property="Foreground"
      Value="{DynamicResource controls-editableForegroundBrush}" /&gt;
  &lt;/MultiTrigger&gt;
  </code></pre>
  
  <p>What do I need to set in my style so that I can change the fore/back color of the displayed SelectedItem - i.e. make the above work?</p>
  
  <p>And I am curious if anyone can tell me why a control like this doesn't use a similar interface as other data entry controls (isn't that the whole idea of polymorphism?) This isn't a big deal, just curious, that's all.</p>
  
  <p>Thanks!</p>