I suggest setting the BackColor
property of the ContentPanel in code after the InitilizeComponent() method is called in your application's form. I think the issue comes from serialization/deserialization of the applied theme. Another thing you can do is to modify the designer generated code by locating the serialized lines where you set the BackColor
property and moving these settings at the bottom of the method after the EndInit method calls where the theme is applied. I have tested it and it works fine.
I hope this helps.
Please let me know if you need more assistance.
the Telerik team