After last night's scan I washed a bit of ultramarine blue into the leaf overlaps. The darkening was considerable and later layers of oxide of chromium pulled the green back. This evening I remembered the new Viridian pigment, a darkish blue-green that worked so nicely. It's a transparent and powerful pigment, somewhat akin to the phthalos. After shading on side of leaves, titanium white with a bit of green made for highlights on the opposing leaf sides.
I think that in general this piece is sliding off to the cool side. Tomorrow I'd like to try warming up the highlighted side with some yellow layers, as well as some white washed to pull the colors closer as well as smoothing things out.