I also like the current style. It all looks very nice Not totally sure about the green background, but it's ok.
You could perhaps attempt to shade one of your scenes and then get some feedback on that. If it were me, I'd go for a slightly washed-out watercolour style, rather than realism. Make it look like the screens are pages from some dusty old book from the middle ages. I'm not saying it's easy, but it means you can get away with adding less detail.
Bear in mind that whatever you decide, you need to be able to create character sprites, menus, etc all in the same style.
Also, you shouldn't underestimate the amount of time and effort it will take to colour all your scenes. Maybe go with what you've got for now, and make any modifications after the gameplay element is complete. If you get too bogged down on graphical details, you risk losing interest and failing to complete the game at all.
Another thing worth noting is that if you have most of the game in this minimal colour style, you can add emphasis to some things by shading it a single different colour. This would be much easier to apply than the infinite detail used in a "realistic" colour scheme, but just as effective (again, as Sketchy said, as long as everything is consistent).
I like your new versions better than the green originals. Not too keen on the more orange-ish one, but I have no real preference for either of the other two.
Of the new 'parchment' style displays, I like the one with the doorway atop the stairwell the most.
Has anyone else here played the "Myth" series of PC games? They had slideshow cutscenes that this project reminds me of. They were essentially detailed line drawings on a parchment page with audio/voice-overs in the background. Apart from being technically superior to the real-time tactical wargames of its day, the Myth series was also one of the moodiest, grimmest, most immersive game series out there.
Gerwin, I recommend you look up the Myth series for some inspiration. The second installment, "Soulblighter," is arguably the most well-done.