Wpf - DataTriggers In Expression Blend?

I have a listbox that displays Shipment Items (custom class) that are formatted using a datatemplate (see below). There is a border element in the template (I am calling it a Gem) that displays which item is active (not selected) which will be the item to which products will be added.

template.png

There is a boolean property in the shipment class (Active) which is set in a click event handler for the Gem element. Normally the Gem is supposed to be dark as in the first image, then lit when active. I have a DataTrigger set up in the DataTemplate to handle the change in the color of the Gem.

<DataTemplate.Triggers>
<DataTrigger Binding="{Binding Active}" Value="True">
<Setter TargetName="ActiveGem" Property="Background">
<Setter.Value>

[code]....

The Gems do not return to their unlit state (which they never were in the first place). They only remain lit.