I don't require it myself but that's a concern, it's nice to have. Maybe someone can build an editor that uses different fonts within one file instead of different colors. Could be something out there for color blind folks already, though seeing no colors at all is unusual. But e-ink has grayscales so you could at least make comments a bit lighter, I think I'd be happy with that.

There's plenty of options available. A coworker of mine used to print out code for reviews. You can use italic, bold and underline as alternative to colors. Grayscale might work nicely for eInk too - for laser printers just thin/regular/bold probably works better.

Other fonts... I could see myself being distracted by changing fonts in a document, except maybe for comment blocks. But for those italic/thin seems to work well already.

Tried to find the tool... it's GNU enscript. Syntax highlighting for several languages, outputs to postscript.

I'd do 3 greys, from lightest to darkest: comments, syntactical cruft like braces, semicolons, certain keywords, etc., and then 'actual' code, variable names and so on.

Much more variation than that with 256 colours is mostly just making it pretty rather than offering helpful distinction imo.