>A blue note is a flattened or sharpened note in a chord, giving it that jazzy or bluesy sound. Can be a fifth, seventh, ninth or thirteenth above the tonic, if you want to get really technical<.
True, but the Hunter doesn't generate a "blue" note in the musicological sense. It's more of a descending tritone (if you're old enough, think of the sound of a passing Vanguard for an aviation equivalent) with a bit of added harmony. Known since the fourteenth century as diabolus in musica and a staple of heavy metal amongst much else.