Green Hat Rule? - Wednesday

Earlier today we were out to lunch with the students and I was wearing my green North Stars hat when I was told by Martin that I should take it off. Obviously I was confused about it and he told me that a green hat symbolizes that my wife/girlfriend is cheating on me and I thought that was pretty funny (I would be a little more worried if I actually had one). That just goes to show that even small things over here that we find completely normal back home can mean something completely different to someone else. I don't think I will be wearing a hat the rest of the time over here though.