Hi Jeff
I should not be to worried about the exact colour! dark green is dark dark in my eyes
, when you have 3 weeks + in the field that would turn that parade Gucci uniform into a riflemans jacket ..
I never paint my whole unit in the same main colour with out darkening some and lighting others , you would never get the same colour cloth .. some would get newer jackets the dies would come out , the quality of some of the suppliers would be better than others ,It should all be taken into account a . then you could look at the weather as well if its just been raining then the rifle green would become darker and lighter in the sun light over a period .
So in my mind, just paint them a dark green and as long as you are happy with the out come you are a winner.
I hope you have great fun painting your brits ,
I myself are working my way through the war of 1812 ! Americans talk about mixed dress !
god i got them in brown, white, grey and Blue and thats just normal Line Battalions dont even go down the road of militia and civ ! units ... all great fun to be had .
Happy gaming brother and good luck with the painting LR..