The two yellows mixed with phalo blue in different proportions will give you a variety of greens but they will have to be toned down with greens´ complimentary colour, which is red; but you can also use the orange to create interesting natural looking greens. i.e. I have used DS hansa yellow medium, DS new gamboge, MG phthalo blue and S translucent orange plus also S red madder dark to push the mix to a darker value. MG phthalo blue and S translucent orange also gives a very interesting dark-valued blue-green. DS perylene green can also be used in shadow areas. For foliage, the most important thing to keep in mind is that ready made greens or even those mixed from yellows and blues should (almost) never be used directly, they will have to be toned down with a red or an orange to create greens that donot look artificial. Just a bit of the red will give a fresher green whereas adding more of red will give you shadow greens.