Thanks everyone,
Regarding the paint, I have done something like 20 very very thin layers of Revell Aqua Color Emerald Green, which is gloss, with a flat brush. It was hard to get the intense green color.
I did some light and fine sanding at some point as well, in order to get a smooth surface. That killed the "gloss" pat.
Then a few thin layers of Future, then some more sanding because it looked slightly milky, then some Future again. Fortunately, that brought this nice shiny finish
I was just trying things, and it feels like a significant amount of luck was involved... I was close to the limit of my patience!
Stephane