It seems that this is going to be a nightmare for developers of Visual Studio extensions, but now with a yearly VS cadence (if not worse with the new VS Updates approach). This post on the Visual Studio blog explains the new changes in icons and colors for the next Visual Studio 2013 version:
Designing the Visual Studio 2013 User Experience
As you see, the UX team keeps insisting on the direction started with Visual Studio 2012, and very reluctantly changes painfully slowly what it was quite evident for many: the new UI introduced by VS 2012 sucks. It lacked borders, it lacked colors, it lacked contrast, and the new icon designs were horrible for many people. What is worse: what was intended “to make the content to stand out”, caused the opposite effect (distraction).
In Office 2013 you get the history repeated: upper case for main menus, and three boring themes (white, light gray, dark gray) rather than two. I bet that at some point a “Blue” theme will be introduced. And afterwards, some more color and borders.
I wonder (and feel sorry) about how many hours were devoted in VS 2012 to change a user interface that was not broken in VS 2010, and now to fix it a bit in VS 2013, while other areas of Visual Studio that provided real value to many users are removed (ex: macros) or frozen (ex: automation model for add-ins, code model, etc.). Not to mention that the performance of Visual Studio is still bad.
Unfortunately, what all this means for developers of VS extensions is that we need to change icons again in our extensions if we want to mimic the Visual Studio 2013 icons.