This help article will demonstrate a step by step tutorial how to customize the ControlDefault theme for RadTreeView.
Open VisualStyleBuilder: Start menu (Start >> Programs >> Telerik >> UI for WinForms [version] >> Tools).
Export the built-in themes in a specific folder by selecting File >> Export Built-in Themes.
Load a desired theme from the just exported files by selecting File >> Open Package
Select TreeNodeElement in Controls Structure on the left side. Then, select FullRowSelect.MouseOver in the Element States section.
Modify the applied fill repository item.
The result is illustrated below. The new fill color is applied when hovering the item:
Save the theme by selecting File >> Save As.
Now, you can apply your custom theme to RadTreeView by using the demonstrated approach in the following link: Using custom themes