In my search for un-metro Visual Studio, I found that the main tool icons for HTML (MVC and Web Forms) and Win Forms are stored as raster resources in a number of unmanaged DLLs. WPF and others are stored mainly as PNG and ICO files in newer managed DLL files. Managed resources are a combination of directly embedded files as well as serialized bitmaps, PNGs, icons, image streams, and binary streams.
Look at these files for most of the toolbar images.
\ Microsoft Visual Studio 11.0 \ Common7 \ IDE \ 1033 \ Microsoft.VisualStudio.Windows.FormsUI.dll
\ Microsoft Visual Studio 11.0 \ Common7 \ Packages \ htmled.dll
Regarding color changes, it seems like Visual Studio is replacing white with black, and also changing the shades of white / gray to a darker counterpart, leaving the rest of the color alone. In past years, they included a leadership style document along with the SDK. I haven't found it in 2012 yet, and the MSDN link still points to a 2010 document.
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