This is jazz, baby.
"Sally's Blues" is part of the "Lost Cues," songs and snippets that were recorded for "Peanuts" television specials, but some didn't make the cut and get into the final film. Having never heard some of these songs before, I was very surprised to see (or hear) just how great and how timeless they are.
Have you ever heard of these Guaraldi tunes: Play It Again Charlie Brown, Centercourt, African Sleigh Ride, There's No Time for Love Charlie Brown, Woodstock's Dream, or Pitkin County Blues? This is jazz at its best. I purchased both albums of The Lost Cues from iTunes. They cost $9.99 each.
They are often quite different from what you would expect for a Charlie Brown theme, but at the same time, very cool, very hip, very melodic, very inspiring to the musical part of your soul.