They aren’t green? But they certainly look green! And I know a few people with green eyes and many more, with hazel eyes.
There’s no melanin/pigment in the iris - it’s sort of an optical illusion having to do with the way light scatters, like the Blue Jay feather. (Blue eyes aren’t really blue, either. Only brown and hazel eyes actually have pigment.)
https://www.reconnectwithnature.org/news-events/the-buzz/nature-curiosity-why-are-blue-jays-blue