Everything should try do some basic syntax highlighting IMO. Not too much, or it just becomes a sea of formatting that doesn't help at all. It is surprising how much difference just a little splash of colour can make if it isn't overdone. If possible, always include configuration options for the user though, so those with colour-blindness issues can tweak things to their needs, those who are just fussy can make the output fit with their finely adjusted system-wide colour schemes¹, and even better, where you can, allow bold/italic/other as well as colours so that those who barely see colour at all can play too.

Of course none of this helps those using screen-readers and other tech, so make sure that all your fancy colouring & such is additive so if it is all “lost” no meaning is absolutely lost with it.

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[1] Some people can be very vocal about this, more so than if highlighting isn't possible at all. If you give any output formatting they'll expect you to match, or be able to be made to match, their preferred style.