Blue Horizon Records, originally founded by Mike Vernon, was a destination for blues fans in the U.K., tapping talents such as Duster Bennett, Chicken Shack, and of course the initial incarnation of Fleetwood Mac, along with classic American bluesmen such as Otis Spann, Champion Jack Dupree, and Elmore James. The label’s first release was “Across The Board,” a 1965 single by Hubert Sumlin, but it wasn’t until 1968 that Blue Horizon really took off, with the debut album from Peter Green’s Fleetwood Mac…