In “Red, White and Blue,” the fifth and final film of Steve McQueen’s Small Axe anthology (and the third to be shown at this year’s New York Film Festival, after the lilting reggae house-party movie “Lovers Rock” and the wrenching social-protest courtroom drama “Mangrove”), Leroy Logan (John Boyega), a British research scientist, figures that he’s had enough of the lonely work of staring at tissue specimens through a microscope, so he decides to become a member of the London Metropolitan Police Force. At his big meet-the-commission job interview, the conversation dances around the issue of race for about a millisecond until Logan puts it right out there, saying that he’s applying for the job “to combat negative attitudes,” and to be a force for change against “divisions” and “misunderstandings.” The crusty officer in charge looks at him and says “You’re right,” and then adds, “Attempts to interact with your people have fallen quite short.”