“Blue notes” are the hallmark of blues melody. They originated as vocal inflections, a slight sharpening of the minor 3rd, perfect 4th, and minor 7th scale degrees that blurred the traditional boundary between major and minor tonality.
For guitar players who use scales as their main reference point for soloing, this nebulousness presents a dilemma when trying to figure out what scale to play when. B.B. King's solos on "Sweet Little Angel" (Live at the Regal) contain all you need to know about exploiting every corner of major and minor blues melody.
To help make sense of it, it's best to visualize blues melody as consisting of two basic shades: "dark blue," represented by the minor pentatonic scale (FIGURE 1, with the flatted 5th, Eb, added to create what is generally called the blues scale) and "light blue," represented by the major pentatonic (FIGURE 2). Combining them puts the whole palette of blues into one scale: the hybrid blues scale (FIGURE 3). Rather than having to choose between this scale or that, you can pick the notes that match the mood you want to create.
If the advantage of the hybrid scale is its inclusiveness, its disadvantage is so many choices. To give it some structure, you need to see it in the context of the chord that usually accompanies it, the dominant 7th (FIGURE 4). The notes of the chord are all contained within the scale, and you can use them as hooks on which to hang phrases. FIGURES 5–8 are typical hybrid licks. The rhythmic emphasis of each phrase falls on chord tones.