Thank you for your interesting question and detailed description of the problem and the steps you perform.
Here are several thoughts on your problem
- The best approach for achieving this is to create custom theme that sets the back color of RadDock (and all needed Control instances such as DocumentContainer, DocumentTabStrip, ToolTabStrip) to Transparent. The problem you are experiencing with seeing the result only at design time is because our theme support will explicitly set the back color to its value that comes from the theme (blue in this case). For more information about our theming mechanism you may refer to this help topic
- The transparency in Windows Forms is simulated - meaning that to achieve the desired effect, a child's parent is asked to paint its portion, overlapped by child, on the child's graphics surface. That said, any transparency will lead to slower performance. The larger transparent areas you have, the slower you application will be.
- If you discard using custom themes then you should know that once you perform some docking operation - e.g. reorder tool or document windows - new ToolTabStrip/DocumentTabStrip instances are created dynamically and you should update their properties respectively in the TransactionCommitted event.
It will be of great help if you can send us a simple skeleton application that wraps the appearance you are trying to achieve.
Please, let me know whether this is of help.
All the best,
the Telerik team