The theming mechanism for our Silverlight controls suite is a bit different from the one in the Silverlight Toolkit that Microsoft provides.
In your UserControl, create a dependency property called CurrentTheme, of type Telerik.Windows.Controls.Theme. Give it a default value of, say, a new instance of the Office_BlackTheme class.
Then, in the XAML of your UserControl, bind the telerik:StyleManager.Theme attached property of every telerik control to the CurrentTheme property of the UserControl. If you change the value of the CurrentTheme property, all the controls that are bound to it should change as well.
Unfortunately there is no easy or surefire way to achieve this. We are constantly looking forward to improving our theming mechanism, but keeping it backwards-compatible and consistent across our WPF and Silverlight suites is no easy task. Hopefully we will be able to implement on-the-fly changing of the current application theme in our StyleManager very soon.
the Telerik team
Registration for Q1 2011 What’s New Webinar Week is now open. Mark your calendar for the week starting March 21st and book your seat
for a walk through all the exciting stuff we ship with the new release!