U can go by statistics or actually live in the area and see who actually lives here. Seattle is definitely whiter than other major cities (+500K) on the West Coast along with Portland and if you only stay in the core of the city, then u will probably see mostly whites. But outside of the city center, especially in the southend u will see a lot more diversity. My grandfather lives in Rainier Beach, one of the most diverse neighborhoods in America. I stay in Federal Way, where u can find every type of person.
Rainier Valley: One Of America's Most Diverse Neighborhoods - Demographic Analysis - Curbed Seattle
But the West Coast is not heavily populated with black people no matter where u go besides Oakland. And yall know about gentrification and how its killing cities with large black populations. So just think what it did to a city where the black populations peak was only 10% in the mid 90s. If u need your city to be 30% or more black then the West probably aint for u.