I know the piece is now finished, but for next time had got thought of turning an off centred or off balanced disc to stand behind the pot. With concentric groves turned on a face plate, you could hint at a rainbow instead of having it as solid form. The problem for me is that rainbows fade at the ends. Your first version was too literal. Indeed the natural attempts as opposed to the coloured painted/stained ones are much better in my opinion.