Which are the notes that define the blues scale as one, what are the "blue notes" exactly. Is the blues scale minor or major?
What is typically called "The Blues Scale" is really the minor pentatonic scale with a dim 5th added. So a formula would be:
1, b3, 4, b5 (or #4), 5, b7, 8
The b5 is generally considered the blue note. However, just my meandering about music theory and culture, This is often played over major chords to give a "bluesy feel". Most often over the dom 7th chord but even over Maj 7th chords. The juxtaposition of the b3 (or b7) in the scale over the 3rd (7th) in the chord creates more tension and this tension is for me the "blue". So one can experiment with multiple "out" notes to generate a very blue sound.