Theme resources These resources are used in the control's default style. Dark theme brushes To change the colors of the control in the dark theme, override these brushes in App.xaml. <SolidColorBrush x:Key="ThumbBackgroundThemeBrush" Color="#FFCDCDCD" /> <SolidColorBrush x:Key="ThumbBorderThemeBrush" Color="#3B555555" /> <SolidColorBrush x:Key="ThumbPointerOverBackgroundThemeBrush" Color="#FFDADAD