There's no doubt that a musician of any nationality or colour can play the blues, and if such an individual has the talent, and immerses themselves in the genre, they will become good - even - great at playing the blues.
But singing the blues? Now that is another matter.
A lot of Britains blues singers are merely doing an impersonation; a very good impersonation in the case of someone like Joanne Kelly but it has to be said that it's not the "real deal".