For the most part Halon is illegal, infact most of the basic fire training courses I have been on have denied Halon ever existed. It was indeed colour coded green and was fitted to 59/0 and 59/1 locos (AFAIK). Halon features in the film Terminator 2, in the big computer lab building. It can still be found on aircraft (if you're gonna die anyway, it might aswell be done quickly).

The reason it was banned was not because it was just as likely to kill people as the fire itself, but because it is harmful to the enviroment.

I found an old Chubb halon fire extinguisher in the back of my shed at the weekend,but its empty......lol....the cylinder is green.....