Obviously, the scene to do is the one where Medea takes Jason into the grove where the Fleece is kept.. Lots of twisted branches and tree trunks, the sun sinking low in the west, and the Fleece glimmering in the light of the torches.
The first design challenge that occurs to me is that the Fleece will over dominate the picture if I am not careful with all that textured, gleaming gold. On the other hand, gold looks better with a dark, rich coloured background, so I can’t just settle for a daytime scene.
I can ease the problem slightly by dressing Jason and Medea in their best clothes, with rich colours and gold details, and perhaps rather than sunset, have it in moonlight (cue a silver kid moon!), with a line of torches to indicate the approach to the grove.
If I make sure that the Fleece has several shades of gold in it, that may also settle it more happily into place as only part of the panel..
There are several books I can use for reference – Tim Severin built a replica of the Argo and sailed and rowed from Greece to Georgia, which is where Colchis is thought to have been. Robert Graves wrote on the subject. I’ll have little trouble finding other references, either. We’re back to myths, legends, and archaeology…