I've always had decent imagination to turn black and white people into color, and the same with buildings, etc.
But somehow I always mentally kept the skies as gray... as if the death and destruction of the war warranted overcast dreary weather, for years on end.
The idea that WWI was fought on many days that were brilliantly sunny somehow makes it even more depressing in a way.
Birkenau (Auschwitz 2), on the hand, was purpose built (Auschwitz 1 was a repurposed barracks) and that really does look like Hell, even on a nice day. Every last part of it screams "this was designed for obscene purposes".
One thing I've been wondering about: Is it possible that the ML algo turns the faces into more "modern" faces because it's presumably trained on later color footage?
You can get dramatically different results depending on your training data set.
The only real issue with that is treating any of the outputs as "realistic" representations in terms of "close to the original scene". It's just a modern interpretation and the viewer needs to keep that in mind at all times.