Listening to the live Q&A after the showing, it turns out that there is about 100 hours of unused B&W footage that's been cleaned up and digitised, but not colourised. In Jackson's own words, he looks forward to higher quality WW1 documentaries being made with it.
Jackson's morbid fascination for state-of-the-art film improvements are breathtakingly OTT and will never help to properly convey the psychological horrors [harm] endured by the soldiers, AKA cannon-fodder.
The technical restoration consisted of scratch restoration, exposure correction, jiggle correction (that's apparently caused by the sprocket holes shrinking). CGI is used to create extra frames to raise the viewing rate from 12fps to the standard smooth flowing24fps, then it gets colourised. Yes, that's all very technically and extensive, but doesn't in anyway detract, but greatly enhances the original intent.
In his words, they've now developed the technology for all archives around the world to use, he'd like to see the 1900 onwards historic archives start to restore old street scenes etc.