Thank you for contacting us.
The “Office2010Black” Skin is designed for dark backgrounds, so we made the color of expand/collapse arrows of RadTreeView control white. If you use white background color in your Web Application, the arrows would be almost invisible. Attached to this thread you can find two screenshots with RadTreeView and different backgrounds.
If this is not the issue that you are currently experiencing, could you please provide me with more information in order to assist you in most efficient way?
Hope this information would be helpful.
If you want to get updates on new releases, tips and tricks and sneak peeks at our product labs directly from the developers working on the UI for ASP.NET AJAX, subscribe to the blog feed