Switch the Windows Forms Designer to a dark background when selecting the dark colour theme
Having a default dark colour theme on Visual Studio 11 is great. The theme, however, hasn't been used consistently across all the different designers. The forms designer, data context editor, XAML visual editor and others have a light background regardless of the active theme.
If the dark colour theme has been selected, use a dark background in all the designers and dialog windows.
This has nothing to do with performance. You should have put this item in the general forum.