We are sorry for the delayed answer. Attached is a sample illustrating a very easy way to change the overlay background. Simply use the OverlayStyle property of RadBusyIndicator.
On the other hand, it is strange you experience any troubles with the default style of RadBusyIndicator. In more details, how did you generate the stylles and how did you "attach" a resource dictionary to the control. I could not reproduce any issue when generating the default style of the control in the regular way in Expression Blend (Object > Edit Template > Edit a Copy).
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!