Yes, that's correct: raw files (with a few exceptions that won't work, those on raw.githubusercontent.com being a notable one).

We could technically inject the library code to colour elements on regular pages, but I wouldn't really know what to colour exactly, it depends too much on the page. Doing all `` blocks could be a thing maybe, or we could imagine adding a feature to selectively colour a block, but there's nothing of the sort supported by the add-on at the moment.