I understand your issues all too well.
I am using a "personalized"
BA colour scheme for my own army. I love the
BA chapter, and was a fan of them back in the days of Space Hulk 1st edition. I've never stomached some of the things their lore has developed into however (Space Vampires?! How about NO), so have just shoehorned them to fit my own vision as I see fit. I could rant about my vision quite a bit, but let's just stick to colour ideas for now..
I do not use any helmet signifier colours at all, aside from gold, which is only worn by the most highly ranking / battle honoured members of the army. The only major variances to red/black/dark metal/dark copper/gold I use are yellow (for 1st ed Space Hulk style hazard stripes and chequered textures on powerfists, hvy weapons, storm bolters etc) and petrol blue (for purity seals, tabards and the like my veterans might be wearing). Petrol blue refersh to greenish turquose in this instance
btw.
For death Company, I use "black metal" instead of regular black. I make it by mixing metallic medium to black paint, just a touch, so that the black gets that metallic sheen but is still dark enough as to not just look like boltgun metal or anything like that.
I also like my other metals and golden stuff looking pretty dark. For chest aquilas I go with a dark gold/brass that is almost closer to tin bitz than copper/gold, but anyone who gets a golden helmet has a bright gold color on the helmet (its supposed to be a badge of extreme honour so its being kept polished etc in my fluff).
I don't think the general "marines are identified by their helmet colour" thing looks particularly good
tbh. It makes stuff look to derpy and smurfy
IMO.
Also, when it comes to the red colour, I am partial to Mechrite Red looking the best colour shade for infantry armour. I've tried many other shades but I always come back to it. It just looks "right"
IMO, not too much like Father Christmas's little elves, its desaturated and brownish enough that it just feels a tad more "serious" to my eye. Khorne Red is almost there too, but its a tad too brown. Perhaps if one mixed certain orange colour to Khorne Red in a right mix ratio, you could get the same shade?
For vehicles, I prefer a red/brown camo pattern instead of just plain flat solid colour. Still experimenting with the right camo shades however. I also use camo on my scouts, not red camo but more like regular camo (grey/green/grown), kinda like how US Marines might look like