Fred Shields and Greg Horner performed the song “Mr. Blue” at Sunday’s Northern Lights Showcase, a tribute to former resident DeWayne Blackwell, who penned the pop hit. As sung by The Fleetwoods, the song reached #1 on Billboard’s Top 100 list in November 1959, and was subsequently recorded by Frankie Avalon, Bob Dylan, and Garth Brooks, among others. Blackwell also wrote the hits “Friends in Low Places” and “I’m Going to Hire a Wino…