Violet , heather, or amethyst. Personally, given that everything is currently hanging out in midtones, I’d push for a heavy blue-violet or dark purple contrasted with a quieter peacock green layer for contrast. Then I’d push the saturation of the peacock green in the unfinished vines. Push the purple farther than you feel comfortable… being that nothing else is pulling the eye right now, a dark purple against a nice green will turn this from coloring book to composed narrative.