Click on the link above that tylerdurden posted, then look at the group of Fett pics that was also posted by tylerdurden, if you look at the top left pic of Fett (the pic which is pointing out info on the helmet) and look at the green on the cheek, thats what the green looks like in real life.
I know it looks blue or grey in some ESB scenes and it looks like its a light shade of green in most pics (the kind of green you might have on your bathroom walls), but its just dark army green and i think they would have just used a few tins of humbrol enamel paint from the local model shop to paint the original helmet, but thats just my opinion of course
Keith.