FlagEnumEditor bug can't change Background Color ?

[Dont]

I am using a FlagEnumEditor in GridViewDataColumn. I want to change the Background color to transparent but nothing happens. Is this a bug ?

The column Statistiken should have the same color as the column Datentyp.

I am using Visual Studio 2013 Theme. 

My source code is here on StackOverflow: How to change FlagEnumEditor Color in Telerik WPF?

 

01.<telerik:GridViewDataColumn x:Name="CheckComboBoxColumn"
02.                            Header="Statistiken"
03.                            IsReadOnly="True">
04.   <telerik:GridViewDataColumn.CellTemplate>
05.        <DataTemplate>
06.              <telerik:FlagEnumEditor BorderBrush="Transparent"
07.                                      Background="Transparent"
08.                                      Margin="-4,0,-2,0"
09.                                      Value="{Binding Aggregates, Mode=TwoWay}"
10.                                      EnumType="viewModels:Aggregates" />
11.        </DataTemplate>
12.   </telerik:GridViewDataColumn.CellTemplate>
13.</telerik:GridViewDataColumn>