>>96408800
>Night Lords were specifically trained to fight on swamp planets. See their heads rising from swamps, the glow of their red eyes coming through the murky water.
swamp terror tactics is a good way to start, but I don't think that alternated scheme helps in that
You could keep the overall scheme very dark and uniform overall and focus on the eyes of the models, eyes of the various demonic faces and iconography on the chaos models, and I think that would be more than enough
or keep the dark iron for everything but the helmet and pauldrons, where a darker color makes the eyes shine more, and which you can imagine being the parts poking out of the swamp