Hello Marianne,
I have fruiting seedheads still green on my arisaema thunbergii ssp urashima, the tubers have gone dormant but the stem is still green and fruits will ripen to red.
I sell these in my nursery, I have 2 left with seedheads on that I can post to you, or if you wish to "borrow" them for painting, let me know what you would like to do.
I can also post you an arisaema consanguineum seedhead if you wish
Pontus