I assume you meant VisualStudio2013 theme as the mouse over color of the scroll bar there is black. However I'm afraid that the only possible solutions here are to either extract and modify the ScrollViewer related Templates (ScrollBarVerticalControlTemplate, ScrollBarVerticalControlTemplate and the RepeatButtons Templates) or to change the theme MarkerBrush as explained here
(however please note that will affect all the other controls in the application).
Hope this helps. If you have any other questions or concerns, please let us know.
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