Here is the first round of testing on the leaves, using chiffon over peau de soie and chiffon over china silk, with hand-painted veins on the leaves:

I don’t like the veins. They are painted in gold on purple and gold on dark red; the rightmost leaf is also outlined in gold. (Click to see the larger version.) The high contrast between gold and purple/red breaks up the color and is visually distracting – it’s hard to see it’s a leaf! The lower leaves, which have much lower contrast, are visually interesting but not overwhelmingly so.
This suggests to me that I do not want a strong pattern or value contrast in the leaves, which narrows the options considerably. I think I will wind up using chiffon over a patterned background; the chiffon will tone down the pattern, making it subtle, but hopefully still visible. (I like to reward the close-up viewer as well as the one who sees it from 30 feet away.) I will use embroidery in a closely related color for the veins.
Since I am not going to my guild meeting after all (was out way too late at a party last night and am too tired this morning to drive 40 miles to San Francisco), I expect to do a lot of dyeing, construction, and surface design experiments today.
Stay tuned for further developments!