You could use a monospace font, the same way that Douglas Hofstaedter distinguishes strings of a formal system in Godel, Escher, Bach. It's poetically appropriate because Hofstaedter was trying to solve the same problem you are: use typesetting to set apart map and territory. 

I personally find colors to be distracting and nonstandard ways of carrying such information.  I like Samuel Marks's idea of using monospace fonts for strings or formalizations as opposed to concepts.  I also VERY MUCH prefer talking about strings vs concepts than map vs territory, as the territory isn't actually available in any text, only different levels of map (in this kind of document; there are other conversations where it makes perfect sense to use map/territory).

Depending on the topic and text, you might also consider physical separation rather than typography as the differentiator.  A column for one level of narrative, alongside another column for a different (more objective) level of description.  Or more humorously, an OOC injection between paragraphs like

Narrator: Dagon thinks self-reference is fun.  Not everyone agrees.

But even more than any specific, I'd love to see some experimentation.  Write a sample paragraph, and try out the 3-4 leading styles.  If you're into it, write a preprocessor that generates multiple styles from the same input, and let readers choose their preference.  

 

If you ever want to do anything particularly weird in an article, you can send me plain HTML via the Intercom and I insert it into the post directly (after doing some basic sanitization). This will make the post usually admin-only editable (if you used any HTML features that are admin only), but works well-enough, and I've done this a few times for articles that really wanted to use color (Beth's AI Safety Debate writeup was one that comes to mind here)

Markdown also supports underline by surrounding the text with single underscores, though it looks a bit like hyperlink. I don't know off the top of my head if LessWrong supports that feature...
if this text is underlined, it does (Edit: looks like LessWrong interprets that as another way to do italic, likely to avoid the hyperlink confusion)

There are also other plain-text options you might consider.

• You could use grouping characters other than quotes (parentheses, square brackets, angle brackets, braces) to distinguish map and territory.
  • You can also use unconventional grouping characters, like literally any punctuation marks that aren't reserved by markdown. Just be sure to test your choices first. I've had some unexpected results involving the $ character on LessWrong in the past.
• There are also several styles of quote marks that might be useful for this kind of differentiation. Guillemets may be especially nice here as you could point them »in for map« and «out for territory».
• You could explicitly tag map and territory statements in a number of ways, as long as you write a forward explaining what you're doing. This kind of tagging carries the advantages of being unambiguous to the reader, easy to remember, and almost certain to be rendered by screen readers. Downside is that they tend to be a bit clunky.
  • You could borrow namespace conventions from any programming language. e.g. map::"thing the map says", territory::"what's really out there"
  • I've seen fanfic enthusiasts compare works with a similar operator:
    e.g. map!"thing the map says", territory!"what's really out there"
  • You could borrow function/method syntax from programming as well. This has the advantage of already being solved for multiple parameters, in case you need something like that.
    e.g. map("thing the map says"), territory("what's really out there", "closely related thing")

My first thought (just upon reading the title) was to use the green hyperlink as one color, but that sounds clunkier than using bold or italics, so I'm not sure it's the best way to go. I would find the bicolor notation very helpful, fwiw, but I'm not colorblind and I don't use a screen reader, so I have no input there (and no idea how a screen reader would process a hyperlink).