Some language teaching software does use syntax highlighting for specific lessons. Rosetta Stone at least does, where it specifically highlights things like noun/adjective agreement, verb conjugation agreement with pronouns and names (
io pag
o, capell
o ross
o [italics for highlighting since we can't color text here]). And then we use various types of brackets, bold, italic, dashes and commas, and other things to isolate what we write. If I want to
emphasize something, on HN, I use a pair of asterisks around the text: *emphasize*.
We use all sorts of typographical conventions to draw attention to the things we want emphasis drawn to or to encode some notion. In many novels, in English at least, a character's thoughts are italicized rather than quoted. The noir detective might be found at his desk thinking, I knew I'd seen her before, but no name came to mind. In textbooks you have a mix of bold and italics used to identify specific kind of content. Bold for new keywords students of the book should keep in mind, usually adjacent to a definition. Italics might indicate a name assigned to something: Using the pumping lemma we can...
Perhaps in our code editors we've overdone highlighting, or coloring could be a poor (certainly for some colorblind readers) method of highlighting, but syntax highlighting itself can make a great deal of sense.
It's worth considering that in the examples from prose, we usually don't draw attention to syntax, but to semantics. What does the thing with different typography mean, why is it given that special formatting or why is it surrounded by special brackets, dashes, or quotes. We don't highlight (as in the example in the article) nouns one way, verbs another, adjectives a third, and adverbs a fourth. Or verbs different ways depending on the tense or number. We highlight individual words in some manner to bring attention to them, or groups of words to indicate their logical separation in some sense from their surroundings.