Hey, I didn't mean to discourage you, quite opposite - plants are fairely simple thing to draw. A few things to consider - fight a brain which naturally tends to put everything in order, in symmetry, apply things uniformly. Plants are rarely like that. =)
I've pulled palette from project i'm working on, it is a bit dull, but in you sample all tones are saturated and fighting for attention, i would say keep saturated colors for that part of leaves which hit with a light and keep shadows less saturated. I don't know much about theory, but it might be true for straight color ramp. Perhaps all saturated might work just as good in shifted ramp. Adarias has quite nice examples in his thread.
