After looking, I'm astonished that this doesn't exist in Emacs. There is a completion plugin using libclang; maybe the highlighting could just be added into it.
On vim's side, YouCompleteMe explicitly denied my approach to integrate highlighting.
I hacked together something to add at least #ifdef highlighting* to YouCompleteMe. It's not quite ready to share due to some bugs, but I'm planning to release it as a patch / friendly fork when I find some time.
I believe there's no reason to have two plugins each running an instance of clang.
* i.e. showing parts of code that are ifdef'ed out in grey
Yeah, that's something I considered from the start. The issue is that, in order for that to work reliably, color_coded would basically need an embedded Python interpreter.
YCM's config file can contain arbitrary python functions and doesn't really need to follow any standards. This makes it hard on color_coded and ultimately didn't seem worth the trouble.
Have you got a plain text version of the highlighted source examples somewhere? I want to compare it with emacs' default highlighting (I think default emacs highlights almost as much as the "After color_coded" screen shot).
So it looks like color_coded can highlight at least a few things that default emacs doesn't: function calls, variables (when they are used, both can highlight declarations) and non-standard type template parameters.
On vim's side, YouCompleteMe explicitly denied my approach to integrate highlighting.