Gary Clark Jr. is not a chameleon. He might seem like one, flipping the Jimi switch to cry out colossal string buzz, then slowing it down with a Clapton soundalike right after. For that reason, it’s easy to peg him as just another blues-guitar virtuoso, as if they’re a dime a dozen. Clark’s true power lies in his restraint. His solos aren’t flashy or overly orchestrated because he came up playing gigs in Austin as a teen, not posting YouTube videos of rehearsed messianic Jimmy Page finger work in his bedroom. Performing on the main stage at Firefly, even in the unforgiving midday sun, makes total sense for Clark, whose music is about as festival-ready as it gets. The sludgy, dripping blues he brings is still captivating because of how he builds to his next movement, especially on the show-stopping “Numb.” Clark couldn’t do it without his masterful band, including a second guitarist dressed like Stevie Ray Vaughan’s ghost, whose technical work was flashier than Clark’s. But that’s the way he wants it. It’s Clark’s swamp; we’re all just gatoring around in it.