In VS 2012 MSFT removed the color for the icons in the UI. Everybody complained on the web. Now the color icons are back. MSFT's spin:

"Visual Studio 2013 includes many user interface improvements based on customer feedback and Microsoft’s core design principle of keeping the focus on the content to deliver an improved user experience. You may notice the more than 400 modified icons with greater differentiation and increased use of color,"

http://www.microsoft.com/visualstudio/eng/visual-studio-2013