If you have ever been to a gathering of military vehicles, you will appreciate that that "service green" colour covers about every shade of green in the rainbow.!!
WW1 military paint was generally darker more glossy shades of green, rather than the WW2 type 'flat' type green chalkboard paint..
Best if you can find a sample somewhere on your bike to match it from ? In a frame tube end, or under the magneto, etc ??
Or find someone with a similar bike, and get a match from them - then you will have 2 bikes in the same shade.
My garage door once came in an 'olive bronze' shade - I went down to the hardware store and bought a can of paint in that colour, and it was quite a good match for a 16h Norton (WW2 era, obviously). Someone has compiled a chart of all the greens they have found on 16h Nortons - even out of the factory they could vary day to day, depending on who mixed the paint and what they had in stock. WW1 era may not be any different ?
So, can you find a sample to match from on YOUR bike ?
P.S. Can you find a good pic of your model back in its day ? A good b&w pic will at least show if it was a lighter or darker green, and probably give an indication of how glossy it was ?
