There is an official standard to BT heraldry. It's it their official codec. Somebody can post the image if they want.
Initiates: white pauldrons, black trim
Sword Bros: black pauldrons, red trim and chapter insignia
Assault: Red trim, black insignia, white pauldrons
Chaplain: black pauldrons, white insignia
Honor Guard: I guess according to the Helsreach videos it's Inities colors with gold trim. I'm cool with that.
Anything else you need the picture. BT nowadays is convoluted garbage so if you want to stick with tradition go with the old dex.
As far as Primaris colors are concerned, it's blue with gold trim. If not, you're doing it wrong.