Don, I assume you are talking about the coloration on your particular SE5 F-904?...I'm not sure anymore which was darker PC-10 or PC-12 but I can tell you that I personally tried to do a color match of F-904 with a printers Pantone Matching System book ( PMS) about 15 yrs ago before they refurbished the plane, ( in the same color again) It was a rather dull cloudy day as is usual it seems in England. There was not dark green in the book dark enough for the book to match it!!
But I did take my own photos using Kodak Echtachrome film to use as my documentation color.
Somewhere along the line of this particular aircraft somebody decided to paint it a very dark green almost black, I have never seen another WWI aircraft with this coloration.