I've never seen any disease that presents itself as green spots. :shock: Based on that, I'm guessing that they may be developing some iridescence as they age. It's also possible these are breeding colors, depending on the type of rummynose you have (there are three possible variants, hemigrammus rhodostomus; hemigrammus bleheri; and petitella georgiae).
If the fish are acting normally, I would say it's some normal process.
If the fish are acting normally, I would say it's some normal process.