Texas has a proud tradition of blues guitar players, from T-Bone Walker and Lightnin' Hopkins through to Jimmie and Stevie Ray Vaughan. Right in the middle of that tradition, hiding in plain sight, is Billy F. Gibbons of the 'rock' band ZZ Top. And not to denigrate rock and roll; fact is, they do rock, no question. But, then, so did the Muddy Waters Blues Band. All I'm saying, don't let their broad appeal mislead you, because ZZ Top is also one of the premi …