I'm pleased with the bases too, they're only Citadel Armageddon Dust, with a wash and a drybrush, then a few Army Painter materials glued on (bits of cork and some tufts in this case).
If you mean the style of shoulder pads on the 3 Eradicators, it's 'Gravis Armour'. If you mean the raised lip on one shoulder of the Assault Intecessors, I've no idea
As for the colour of the equipment on the unhelmeted marines, I just painted it how it felt right to me, I kinda figured it looked like the stuff that would normally be 'under the armour' so wouldn't get painted a colour, it'd just be black/silver as if made out of (super space age) plastic and metal. I wouldn't get too hung up on exactly how you 'should' paint certain things, especially if they're of no consequence to anything gameplay wise - I guess general colour scheme can impact if you want to game as specific factions but I don't really play the game, so no idea how uptight people would get if you wanted to play as 'Ultramarines' but had painted them Purple and Silver or something.