After adding a reference in the designer (in a regular field or within the RTE) you cannot tell where this reference is comming from, you just have the name of the reference.

This is very troublesome if there is an item property call "foo" as well as a variable called "foo" and maybe even a common property "foo".

So far I try to prefix all my variables with "var" so I can tell them apart, but that doesn't feel right.

I would love to be able to tell the different source apart by having the references color coded im some way.

Alternative you could also provide a tooltip that would show up upon hover that might show "{WorkflowVariable:foo}" instead of just the "foo". I think that would help very much when working with existing workflows.