I asked around a number of places this same question in a number of different fashions. I get where you're coming from - this is 30K, and in a lot of senses, it's almost more of a historical wargame than a spin-off of
40K. There's a lot more playing to fluff rather than inventing your own going on - it's a tighter space, creatively.
With that said, Space Wolves.. don't seem to have anything set in stone, beyond a left pauldron being plain grey with a red wolf head sigil. Even the Inferno book, which shows a Grey Slayer in MkIV armour (where the general consensus is that MkIV was more common on the Traitor Legions) and a panopoly of right pauldron designs citing specific units in specific companys or weird niche cases rather than anything complete and definitive like Ultramarine's have.
The general consensus is 'whatever', which I guess can be a little unnerving. I've read a good deal of Book VII: Inferno, as well as both A Thousand Sons and Prospero Burns and found no mention of it. I heard there's a couple of Audio Dramas (one of which even features Geigor, the
one special character model we actually have other than Russ who wasn't even mentioned in the main Horus Heresy books and I'm definitely totally not butthurt that we didn't get pre-Dreadnout Bjorn no siree not me not at all), but I haven't heard them yet so I can't comment on whether they make mention of it.
What I do have, is two photos from ForgeWorld products.
Here and
here. One of which depicts a Grey Slayers with black and red triangles Grey Hunter style with some fancy runic lookin' Tactical Squad arrow, and the other is a second plain grey with some sort of company sigil, possibly?
For what it's worth, I will generally do triangles on my shoulders. Red and Black for Grey Slayers and other basic Troops, Red and Yellow for Fast Attack units and Jump Pack marines, White and Black for Heavy Support and other Heavies, Yellow and Black (predominantly yellow) for Elites and Veterans, and Yellow and Black (predominantly black) for
HQ/command characters. This is basically just the Heraldry typically used in
40K, and I reason using it as.. well, it had to come from somewhere, maybe my dudes were among the earliest instigators of this pattern?
You've definitely got a few options available to you. If you want to be
super safe then I'd just leave the right pauldron plain grey like the MkIV Grey Slayer pictured in Book VII: Inferno - otherwise, black and red is a pretty good call. Possibly, given the black shoulders 13th Company used during the Eye of Terror campaign back in 3rd/4th Edition
40k, plain black might also work? If you're like me and
kinda fancy getting a bit of variation in colour, do the classic Space Wolves scheme, or just go nuts. There's a whole lot that's set in stone in 30K, but the heraldry of The Rout is most certainly not.