Thank you for writing.
The orange color of the shape in the Visual Style Builder's EditRepositoryItem dialog is solely for visualization purpose. It has a distinctive color for better contrast with the background. If you want to change the color of a border of some element you have to edit the border repository that is applied to this element.
I hope this will answer your question. If you need further help I would be glad to provide it.
All the best,
the Telerik team
Explore the entire Telerik portfolio by downloading the Ultimate Collection trial package. Get it now >>