Ruth Negga and Joel Edgerton portray Mildred and Richard Loving, the real-life interracial couple at the center of the landmark 1967 Supreme Court case Loving v. Virginia, in the upcoming movie “Loving.” Negga, who also stars in AMC’s “Preacher,” says it was “a beautiful thing” to prepare for the role by watching the real-life Lovings interact in archival footage.