If you can't use them as normal variables (which you can't with superglobals), yes. (Reserved) Keywords and other language constructs should, in my opinion, not have the same colour as variables. Maybe you could add a colour option for "real" keywords (return, public, function, namespace, use, ...) and another for pseudo variables ($this, $_GLOBAL, ...). It would however strike me as incredibly odd if $this and parent had a different colour.