Need Help with Styling a GroupBox

Hi

I defined a Style in my XAML to be used on all Groupboxes, but there's ONE groupbox's background property that has to be different from the others. I tried setting this property in the code-behind, but no luck. Any ideas?

Here's the code for the style:

<!--A style that formats all groupboxes-->
<Style TargetType="GroupBox">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="GroupBox">
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="Auto"/>
<RowDefinition Height="*"/>
</Grid.RowDefinitions>
<Border Grid.Row="0" BorderBrush="White" BorderThickness="2,2,2,1" CornerRadius="0,12,0,0" >
<ContentPresenter Margin="4" ContentSource="Header" RecognizesAccessKey="True" />
</Border>
<Border Grid.Row="1" BorderBrush="White" BorderThickness="2,0,2,2" CornerRadius="0,0,0,12" >
<ContentPresenter Margin="4" />
</Border>
</Grid>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>