This is from a red-headed friend who passionately denies ever having committed murder.
It was Navi class. We were starting to learn about David HaMelech. And the teacher clearly had this anti-red-hair speech as part of her lesson for many years, as she just launched into it. The entire class went dead silent and all stared at me.
I just looked at her solemnly and nodded in agreement. I was trying to convey “That’s how it is. I have a very murderous and passionate nature. And here you are, insulting my people. Hmm,” with my eyes. But I probably just looked kind of sleepy.
Red is the color of very passionate feeling, which is naturally used for doing Esav-like things such as murder. But — if a redhead tries really hard, they can channel their bloodlust into something positive, like becoming a shochet or a mohel or defending klal Yisroel, and end up like David HaMelech.