Nobody gets any bluer than ... Mystique!
Kidding ...
In the blues guitar idiom, I think it's more of the combination of articulation, dynamics and vibrato that makes any particular player stand out among the rest ..
So, it's not a question of how many notes you play. It's more a question of how well you play that one note..
Offhand, I'm reminded of SRV's 'Tin Pan Alley'.. that song stands out because it's such a glaring analogy of how he makes the transition from near-whisper volume and just blares out with that stinging line ... it's like 'Yow!!! What the ***k was that?!?!"
Or, in the sax realm, there's David Sanborn who, to my mind, has the most distinct vibrato .. now, my point of reference is an old song of his 'Carly's Song' (dedicated to Carly Simon, if I'm not mistaken) where he comes up with what to me sounds like the bluest sax lines ever ..
What makes them blue?
I would say it's the control ... having absolute control over the volume and intensity of a note at ANY time ..
Hmmm ... but let me reconsider what I said earlier about number of notes..
George Benson comes to mind.. Now, here's a jazz guitarist who doesn't bend strings the way most blues guitarists do.. But even then, the way he slides in and out of the blues scale gives his playing that 'blue' touch ..
Even his solo in 'Breezin,' a characteristically uptempo I-VI-II-V pattern, starts sounding bluesy midway through..
Does all that make sense?
Just to recap, it's articulation, enunciation, dynamics and vibrato ...