You can find all 24 system colors here . Also on the same page there are high-contrast colors of the system, as well as special SystemAccentColor
At run time, this resource ( SystemAccentColor ) receives the color specified by the user as the accent color in the Windows personalization settings.
Almost all system brushes are defined here . Please note that this link is based on Windows 8.1, and it skips several Brushes like PivotForegroundThemeBrush .
How do I know? This is how I find all the system colors / brushes -
Colors - Properties> Brush> Solid Color Brush> Color Resources 
Property Brushes > Brush> Brush Resources 
Hope this helps!
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