Comment by tmtvl

A colon in Guile is just a regular character. For example:

  (define abc:def 3)
  (define :ghi 4)
  (* abc:def :ghi) ; => 12

In Common Lisp a colon is a package separator, with an optional package which defaults to the keyword package if not given.

  (eq :foo keyword:foo) ; => t

I don't know about Clojure or Racket because I don't know much about Clojure or Racket. I know Clojure differs in various ways where syntax is concerned to Common Lisp or Scheme (I do like the idea of using square brackets to visually indicate that a collection of atoms may not represent a function call, I hate the idea of the comma being a whitespace character) and that Racket has different languages (though I don't know what that means in practise).

That said, I don't quite know what to think of your third sentence:

> Clojure tends to use them very heavily though, and last I looked it seemed like Racket used more lists

I suppose them refers to keywords? But Racket uses more lists compared to how much Clojure uses keywords? As lists have more uses than keywords that seems likely, though as I said: I don't know anything about Clojure or Racket apart from Racket once being called PLT Scheme.