Far Northern Attire

[Iscah]

do they own blue colour now? red? weaved decorative laces and borders, embroidered details? gloves, belts, beanies?

They're not trying to "claim the colour blue", though. They're claiming a specific combination of features that, evidently, people see in combination and say "hey, that's a Sami costume" and not "that looks like they referenced things like Sami and Nenet costumes". (In any case, they would be quite geographically close and presumably culturally linked? And I don't think they're going to mind another traditional culture in the same way they're going to mind an international company profiting off their cultural designs.)

Again, if you're building a "far northern" costume for a fantasy setting then it makes far more sense to me that you would research multiple real-world cultures from that climate, work out the common elements and add some invented specific details to the embroidery and colour scheme, rather than taking a single distinct cultural dress and dropping it straight in.

And if you know it's going to upset people from that culture, all the more reason to avoid it – at the most pragmatic level, to save on drama, even if you don't personally care about their feelings.