System.Windows.Media.Brushes の各ブラシをSystem.Windows.Media.Brushesの各スタティックプロパティの SolidColorBrush のColor 一覧で調べたので、ついでに System.Windows.SystemColors のブラシの色一覧を調べてみました。

Windows Server 2012 , .NET 4.5 で確認したので、他の環境で変わるかもしれませんが。

 
rgba(0,0,0,1)
ActiveCaptionTextBrush
 
rgba(0,0,0,1)
ControlTextBrush
 
rgba(0,0,0,1)
DesktopBrush
 
rgba(0,0,0,1)
InactiveCaptionTextBrush
 
rgba(0,0,0,1)
InactiveSelectionHighlightTextBrush
 
rgba(0,0,0,1)
InfoTextBrush
 
rgba(0,0,0,1)
MenuTextBrush
 
rgba(0,0,0,1)
WindowTextBrush
 
rgba(0,102,204,1)
HotTrackBrush
 
rgba(51,153,255,1)
HighlightBrush
 
rgba(51,153,255,1)
MenuHighlightBrush
 
rgba(100,100,100,1)
WindowFrameBrush
 
rgba(105,105,105,1)
ControlDarkDarkBrush
 
rgba(109,109,109,1)
GrayTextBrush
 
rgba(153,180,209,1)
ActiveCaptionBrush
 
rgba(160,160,160,1)
ControlDarkBrush
 
rgba(171,171,171,1)
AppWorkspaceBrush
 
rgba(180,180,180,1)
ActiveBorderBrush
 
rgba(185,209,234,1)
GradientActiveCaptionBrush
 
rgba(191,205,219,1)
InactiveCaptionBrush
 
rgba(200,200,200,1)
ScrollBarBrush
 
rgba(215,228,242,1)
GradientInactiveCaptionBrush
 
rgba(227,227,227,1)
ControlLightBrush
 
rgba(240,240,240,1)
ControlBrush
 
rgba(240,240,240,1)
InactiveSelectionHighlightBrush
 
rgba(240,240,240,1)
MenuBarBrush
 
rgba(240,240,240,1)
MenuBrush
 
rgba(244,247,252,1)
InactiveBorderBrush
 
rgba(255,255,225,1)
InfoBrush
 
rgba(255,255,255,1)
ControlLightLightBrush
 
rgba(255,255,255,1)
HighlightTextBrush
 
rgba(255,255,255,1)
WindowBrush