Hey Ian,
Looks like you almost had a second one in the UL forming too! The rainbow stands out nicely against the dark and stormy BG and yo uchose it's placement well. You did well minimizing the FG.....and while it isn't the most interesting....it does work and you have minimized it appropriately. I would remove the white thing in the central right FG.....but given what you were working with I think yo uhandled this quite nicely!
Thanks Rene and Roman. I think there are a bunch of rush-hour drivers still cursing me. Yes, a second arc was forming on top. Before I moved here 11 years ago, I had never seen a double rainbow. Now I've seen many and a rare triple. I agree about that white thing -- I'll clone it out.