Watch the BB Diminished online guitar lesson by Jeff McErlain from 30 Sweet Blues Licks You MUST Know
My hubris was somewhat surprised to hear BB King use a diminished arpeggio on a recording. Surprised because of my own preconceptions of what his musical knowledge was, so I was being a jerk!
Anyway, BB knew what he was doing well beyond what he was using on his tunes, I was happy to learn. Why happy? Well, he played for the music and played what he heard on that music. There is a depth to his playing that I used to take for granted. It's like Hendrix: I grew up hearing him my whole life, but I remember the first time I really "heard" him. It was a truly life altering experience. I had the same experience with BB.