Microsoft released a new version of ASP.NET Web Tools for VS 2012.
After installing syntax highlighting is back again.
http://blogs.msdn.com/b/webdev/archive/2013/11/18/announcing-release-of-asp-net-and-web-tools-2013-1-for-visual-studio-2012.aspx
Installing VS 2012 Update 4 was not enough.
A set of offline installers is available. The offline installers are easier to use than the Web Platform Tools invoker (WebNode11Pack.exe @ ~114KB):
If you want an offline installer then please goto http://www.microsoft.com/en-us/download/details.aspx?id=41532
- AspNetWebTools2013_1Setup.exe @ ~39MB
- WebToolsExtensionsVS.msi (for Visual Studio 2012 standard edition[s]) @ ~21MB
- WebToolsExtensionsVWD.msi (for Visual Studio 2012 free “Web” edition[s]) @ ~21MB