Our Open Studio group had a workshop about two or three years ago given by ( I believe) Nancy Howell (past President of Massachusetts Watercolor Society) in which she gave the following advice for GREENS.
Know your blues and yellows.
Dark to light BLUE, depending on amount of red, is
french ultramarine, cobalt, cerulean, in order
Dark to light YELLOW,
yellow ochre, new gamboges, lemon yellow
LIGHT GREEN__________lemon yellow, yellow ochre, cerulean
MID-VALUE GREEN______cobalt, lemon yellow
SLIGHTLY DARKER mid value G __cobalt, lemon yellow, french ultramarine
DARK GREEN__________french ultramarine, new gamboges
DARKER GREEN________french ultramarine, new gamboges, transparent oxide red
Ad violet to darker green to get branch color.
For Pines, use violet and transparent oxide red for branches.
I do not like BLACK, so I use Alizarin Crimson and Hooker's Green unless I really want a cool black.
I've been studying trees for quite a long time. It is nice to see this thread.