I live an hour south of Boston and have spent a lot of time in the city. The city is mainly divided by neighborhoods of varying cultures and ethnicity. For instance, a huge bulk of Boston is China town, so it wouldnt be a huge stretch in your story to add some Asian characters, include their culture, and maybe even some of their lore of your characters need help with the spirits.
There are entire blocks of stickly people of color, African americans, dominicans, hispanic people.
And yes, there are a lot of white people but they are mostly there for business, work, and travel and the majority of them commute.
The outskirts of Boston is mostly low income and fairly slummy. I mean places like Quincy and Dorchester. They are within a short drive from boston and are populated by mostly people of color.
I also want to note if the theme of your book that you are passionate about is focused around one culture, dont feel ashamed for not including others. You dont want it to seem forced just to be politically correct or gain ethnic brownie points ya know?
However, there will be plenty of black people, asians, hispanics, and white people living in boston both scattered and focused in various neighborhoods.
You could take the time to focus on the spiritual sides of the asian and african cultures as well.
