Bleaching is to mainly remove tannins, to make the paper white, and to stay white over time. It also makes the paper better able to absorb and retain ink. You don't need any of those properties if you're printing in white, because you can't use absorbent type ink in something like this, it won't show well. You could dye in lieu of bleaching (and this might be cheaper actually).

Printing the text is the challenge. The ink has to be on the paper instead of in the paper... The methods required to do that and come up with a quality product have existed for a very long time, but they'd be methods used to create high end things like wedding invitations and greeting cards and not bulk products like books. I believe the first tech that could do this economically at scale was the photocopier (maybe mimeograph?), which basically melts plastic onto the surface, and could apply clear white text onto black paper as easily as black on white.

I would imagine though, that the tech that could do this in the most economically viable way, would be to ablate the text in with lasers, similar to thermal printing. That would actually reduce the consumables used, maybe even by a lot. likely would overall entail much less hazardous/caustic consumables too... Dark mode printing could possibly be incredibly "green" :)