I found a flat green color that was part of a "Camoflage" color spray paint set. I used it on all the fronds, and then added back a little depth with a darker green wash. The trunks I did sort of the reverse, a dark brown spray and drybrushed with a khaki. If you are building a jungle, then spray paint is the only way to go. I also used lots of aquarium plants and different sizes of palm trees., even those little cake decorating ones.
Good luck