We shouldn't be adding VS specific stuff to XmlCore - it's meant to be indepedent of VS. Can you put your code in EntityDesignExplorerFrame instead?
XmlCore\Themes\Aero.NormalColor.xaml
Related Items:
http://entityframework.codeplex.com/workitem/653
http://entityframework.codeplex.com/workitem/331
XmlCore\Themes\Aero.NormalColor.xaml
Related Items:
http://entityframework.codeplex.com/workitem/653
http://entityframework.codeplex.com/workitem/331