Hi Rav,
You can view your custom theme in design view if you set it explicitly on any control. When you set an application theme Blend is unable to render it in the Design view, but for testing purposes you can set the custom theme in the regular manner. The following will show a Metro styled RadComboBox in Blend:
I hope this will be helpful.
Best wishes,
Dani
the Telerik team
Explore the entire Telerik portfolio by downloading the Ultimate Collection trial package. Get it now >>