Thats a really good question. I've never seen one that I am 100% is original in color. Most that I've seen that look period were black-ish, almost bare metal. I'm pretty sure this would be the correct color, but I'm not sure enough to bet money. I've seen red ones, yellow ones, some kinda whitish in color. Some with stripes, some without.
Same with HE; I've seen those in yellow, grey, etc. When you are talking 100 yr old shells, even a repaint from the 30's looks pretty old at this point. I don't have books, I've just owned probably a dozen of them in different varieties over the years.