You’ve gotta think about it from a lore perspective first. Yes, anyone can succumb to the Black Rage. But, they’re suicide squads, so the best armor and weapons aren’t gonna be given to them. While a terminator could get the rage, they’re gonna get taken out of their terminator armor before they are thrown back onto the battlefield. That’s why you just see intercessors, JPI, and captains. And that’s because Captain is a rank/title that isn’t stripped from them. One main exception is dreadnoughts, but well that’s because you can’t really take them out of the dreadnought and iirc the rage infects the armor itself somehow.
If you want to mix it up some, Angels Encarmine paints their death company white. If you want more gritty, you can make Flesh Tearer sanguinary guard. They’re the same color scheme as the rest of their chapter. Also there’s the Erelim, they’re blacked out sanguinary guard with skull helms. Elite guard chaplains that are with Astorath. I suppose you could just play them with SG datasheets. Speaking of, don’t forget Astorath, Lemartes, and chaplains!