Reddad, any of those colors would work. I have seen leaves painted all kinds of colors that aren't in nature. Some of the smaller leaves make great pieces inside the house too. That's what I want to do next, small ones that are more bowl shaped to hold things. It's just been too hot to be outside for too long.
When you are making these leaves, you can put hooks in the backs of them (weight appropriate) to hang on walls when they're finished. In order to make them more bowl shaped, you need to mound up the sand you are curing them on so they will be 'cupped' when they cure.
And the paint I use is just cheap acrylic paint in the craft section at Wal Mart. I like the matte sealer the best when they are totally finished. I use little tiny brushes for the veins and when I apply the sealer I use the throw away foam brushes.