S T R U C T O R I Z E R - User Guide
Settings > Highlight variables?

Generally, all text in the diagram elements is written in standard font (black), but you may enable the option "Highlight variables?" in the menu "Diagram". This does not only highlight variable names, but also operator symbols, string and character literals, and certain keywords (also see page Syntax highlighting in the Features section and page Parser Preferences):

Diagram menu with highlight option selected

Alternatively, you may press <F4> to toggle the highlighting mode.

Here is an example for the effect:

 

standard diagram versus highlighted diagram

 

You will find further examples throughout this user guide and, of course, in practical use - it's quite straightforward.