[martinced]

Clojure puts the emphasis on functional programming and the context should hardly ever be "global".

So I don't think it would make much sense: the context is the sexp you're currently in (recursively of course) and that's it. Sure it may help a bit if you're inside, say, a let and have a "long" function: so you'd be on a "var" (they're not vars but bear with me) and that same var would be highlighted inside the let. Why not but... You do know anyway that it cannot come from anywhere else because you shouldn't be using globals in the first place.

I do certainly try to only write referentially transparent Clojure function so this kind of coloring really wouldn't help me a lot.

Now of course there is an Emacs minor-mode which does modify the background of each sexp recursively inside your function should you like such a thing. (I'm personally fine with indentation and rainbow parentheses but YMMV)