Daniel, Hard headed adherence to an old tradition? Seriously, I do believe BOCA says Green, but here in VA we use Red, but over in Md the use green.......yup, it's confusing.
Each jurisdiction, of course, has the right to amend the code as they see fit. Since you asked the question on Sunday, you'll have to wait for proper codes until I hit the office tomorrow. In all truth, the answer is in the first sentence even with tongue in cheek. I'll give you some more pro-fish-in-all answers in the AM, unless someone with books at home wants to tackle it today.
OK, 96 BOCA says: "Exit" signs shall have red letters at least 6" high...." So I was wrong, it was red. ICBO - 2000 says NOTHING about color (smart guys) 1003.2.10.2 says 6" letters in high contrast. Now ya got me curious as to where the danged green comes from.
George, I think you are right when you said that some states/jurisdictions have adopted red and some green. Check with your local Hubbell Lighting Rep. If he doesn't know, he can find out. Many years ago, I did a design project in Ca., and I remember that was the only time I have specified green letters. I think most states require red.
I was at the movie theater (one of those multi-plexes with the stadium seating) last weekend and noticed the color of the exit signs. The ones over the outside doors were red. The signs over the doors about three quarters of the way up had green signs. Using that exit would take you down a flight of stairs and then down a hallway to the outside door that had a red sign. Seemed to make sense to me.