They have definitely embraced the red and black colour scheme:
https://nhlseattle.com/
https://twitter.com/NHLSeattle_
I find that odd since there are some cities that just seem synonymous with particular colours, like Calgary with red.
When I think of Seattle, green and blue are the colours I think of. They probably want to avoid that because of the Canucks, but they could vary it enough to be unique from the Nucks.
The Sounders use blue and green but no one would confuse their colours with the Canucks...