This article demonstrates how to customize the default theme of RadDock:
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
Navigate to RadDock in Controls Structure on the left side. Then, expand to and select ToolWindoCaption. In the Elements window select ToolWindowCaptionFill.
Modify the applied fill repository item.
Save the theme by selecting File >> Save As.
Now, you can apply your custom theme to RadDock by using the approach demonstrated in the following link: Using custom themes