I remember as a kid pinching people today who were not wearing green. Wikopedia states that the color for St. Patricks Day was originally blue. It's good they changed it because we don't want kids having a blue day.
Ellen is always asking me my favorite color - at least 60% of the time I spontaneously respond green. However I don't have much green in my wardrobe as I picked out an outfit to avoid getting pinched today. So why green?
Maybe the subconscious idea of the slang term - "Give me some green". At Accenture we called the staff "green beans". My business and SVP's focus area is environment - so maybe green enters the picture there.
But in the spectrum mnemonics-- green is right there in the middle with it's own initial.
Roy G. Biv