Almost a year ago, I took the liberty of signing up for an online class about Hary Potter, and there were discussion on the evil connotation of green. It's a pity, though that I wasn't able to save the lecture abut it, but I remember it being mentioned that a person born with green eyes being typecasted as evil in ancient Ireland.
I think green is as natural and as unnatural as it gets. The mere sight of green can calm stresses eyes, but veiwing under green lights is scary. I mean, I was brought up by cartoons whose villains were living in green-lit dungeons. What is more freaky than that?
I guess it depends where green is most fit to be seen, or, where we think green fits in the scenery.
btw, I tried SpM's
survey of disgust link, and it makes a lot of sense. Blue is associated with disinfectants, and so we are more likely to touch something blue that something yellow, which reminds most people of puss.