Now for my little tests...
As expected, a mixture using Quinacridone Gold instead of Cadmium Orange lent to transparency. The resulting greens are quite similar.
Many artists don't use green at all but mix from blues and yellows so I thought I'd try that here. Not bad, reasonable, but a bit limited in range.
Also read that sometimes siennas are used. Although labeled as burnt sienna, this is really raw. Again, somewhat reasonable. Below is our same Thalo Green Yellow Shade, this time with Dioxazine Violet. This mix went straight to bluish and very dark. Useful in its place but not here.
And lastly, our same green mixed with Cadmium Yellow. Really too close to yellow to veer off the desaturated path.
These exercises have been most useful. I feel like there is hope for getting at least close to the coloring of Vinca leaves. I have concentrated on the tops but I don't expect much trouble with the undersides. And now I have some ideas on dealing with flowers. Next up would seem to be assembling a few sketches with coloring. Sometime in the future I must dig into more detailed studies of green mixtures, something along the article Mixing Green within Bruce MacEvoy's incredibly rich and deep Handprint web site.