I'm interested in this as I have red hair. And it has come up elsewhere.
I've had partners that are almost fetish-like in their red-haired devotion. I've also come across people who say "oh, are people scared of you because they think you are deeply, seriously big with your emotional state ?"
ie. an expectation that all may be extreme (anger, passion etc). I'm interested in sterotypes I guess, and investigations as to basis of them..
And there are some interesting studies about pain thresholds etc. It does seems weird, but there may be some genetic differences when it comes to us. I've also read of it being a "defective" gene...
And you only need to change a few letters to make that word "effective"