title: Trying to set the Background of a combobox in WPF
body: <p>I am customizing how my validations show in my WPF application.  I have a single style.xaml for my application and most of my control styles look like the following textbox style.</p>
  
  <pre><code>&lt;Style x:Key="TextBoxInputField" TargetType="TextBox" BasedOn="{StaticResource TextBoxFieldBase}"&gt;
      &lt;Setter Property="ToolTip" Value="{Binding RelativeSource={RelativeSource Self}, Path=(Validation.Errors), Converter={converters:ValidationErrorsToErrorMessagesConverter}}" /&gt;
      &lt;Setter Property="Background" Value="{Binding RelativeSource={RelativeSource Self}, Path=(Validation.Errors), Converter={converters:ValidationErrorsToBackgroundColorConverter}}" /&gt;
      &lt;Setter Property="Validation.ErrorTemplate"&gt;
          &lt;Setter.Value&gt;
              &lt;ControlTemplate&gt;
              &lt;/ControlTemplate&gt;
          &lt;/Setter.Value&gt;
      &lt;/Setter&gt;
  &lt;/Style&gt;
  </code></pre>
  
  <p>This sets the tooltip and the background according to whether or not the bound property has validation errors.  But when I try something similar with the combobox style the background is set according to Snoop, but the combobox does not appear yellow in the UI.</p>
  
  <pre><code>&lt;Style x:Key="ComboBoxValidation" TargetType="ComboBox" BasedOn="{StaticResource ComboBox}"&gt;
      &lt;Setter Property="Background" Value="{Binding RelativeSource={RelativeSource Self}, Path=(Validation.Errors), Converter={converters:ValidationErrorsToBackgroundColorConverter}}" /&gt;
      &lt;Setter Property="ToolTip" Value="{Binding RelativeSource={RelativeSource Self}, Path=(Validation.Errors), Converter={converters:ValidationErrorsToErrorMessagesConverter}}" /&gt;
      &lt;Setter Property="Validation.ErrorTemplate"&gt;
          &lt;Setter.Value&gt;
              &lt;ControlTemplate&gt;
              &lt;/ControlTemplate&gt;
          &lt;/Setter.Value&gt;
      &lt;/Setter&gt;
  &lt;/Style&gt;
  </code></pre>
  
  <p>What can I do to change the background of the combobox to show in the UI?</p>