Please note that Blend can extract only the default theme. This is why you get our Office_Black theme after extracting the default template of our controls. In order to overcome this behavior you can use implicit themes. For more information you can refer to this article
. Following the approach described in the article, you will be able to set and edit the Windows8Theme. Furthermore, in order to change themes at runtime you can follow the approach described in this article
Please give these suggestions a try and let us know if you have any other questions.
Pavel R. Pavlov
the Telerik team