What allows people to know if a black person is talking, even if they are speaking standard English? They aren't using a separate dialect, nor have an accent, yet it's easy to know if they are black. I know some black people speak very well and it's impossible to know their shade. I tried researching, but only found this referencing a dialect, from "www.psychologytoday.com."
Numerous traits in speech provide clues to someone's background, be it accent, vocabulary, phraseology, or tone. These clues can be completely wrong, but they are also often right, based on the experience of the listener. Think of the stereotypical Scottish, British, American, Indian, South African, or Australian expressions of English, and it is not difficult to distinguish regional variation within, e.g., AmE that includes some racial or socioeconomic clues about the speaker's background. Such clues are often incorrect, because (I trust) social mobility is real, but we are all products of our upbringing. All of this is (I hope) rendered moot when we see the universal expressions of commonality in high-point moments like Michelle Obama's speech at the Democratic National Convention in Philadelphia in July 2016.