Thanks for the advice!
I played around a lot more and found out that having just the shoulder trims without armor trim looks rather stealthy. Whereas with full gold trim, it seems to look better with a brighter blue, again based on
this Konrad Curze pic. I'm aware that the pink in that pic is probably due to lighting or just artistic preference, but it shows that the color scheme works, I think.
So for the ostentatious Lords and Champions:

or
And regular marines may look more like:
I try out Royal Purple
but I don't think it works well. I think the Red in the original
NL color scheme is important in conveying a sense of blood and death. Changing Red to Pink lessens that feeling but is still a terrorizingly in-your-face color, that looks like a Slaaneshi perversion of the redness of blood (if that makes any sense). The purple version seems to be a lot less striking.
I'm quite aware that the
NL don't approve of Chaos worship, though I appreciate the warning. But you don't choose when you get corrupted by Chaos, case in point the Death Guards and the Destroyer virus. So First Claw wants my head, who cares :p
Plus I always like to be a little unique (often my undoing). A *little* twist seems to spice things up. I also had the idea that there would be two (political?) factions in the warband... One group that is pro-Slaanesh, while the other is the staunch anti-Chaos-worship type. That doesn't really work if they get corrupted while travelling through the warp. Unless the latter group was deployed at the time?
Edit: Actually I just realized... The Night Lords basically have the worst recruits - gangsters, thieves, murderers. You'd think they'd be the first to be Chaos corrupted. I suppose the ones that hate Chaos worship are probably Terran. I read somewhere that the
NL were originally for Khorne, but I don't really want a one-dimensional
CC army unfortunately.