The classical Latin word for a rainbow seems to be Iris (Iris or Iridis, f.). Did the Romans ever list or otherwise discuss the colors of the rainbow in extant literature?
I asked about colors in classical Latin earlier, and I got a nice answer. The matter is complicated. I just realized that rainbows look the same now as they did two millennia ago, so if the Romans named the colors of the rainbow, then we could be exactly sure about those colors and see them as they did.