It went to colour roughly 15-20min into it, and added to that, and the commentary which was recorded by still living veterans (as Peter Jackson said in interview, let the veterans tell their own story in their own words) of the conflict in a BBC series from the 1960's, was the albeit perfect soundtrack added by using forensic lipreaders. The footage was analysed for what the soldiers were saying, then where possible, capbadges were identified, and voice actors were used with the same regional accents. Battle soundscape was added where appropriate, and (for me) for the first time, the old speeded up black and white silent footage literally transformed and brought these ghosts to life, seen by us like this for the first time..
The last credit on the programme was poignant:
"Filmed on Location on the Western Front, 1914-1918"