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
Many thanks for the link and the info; very interesting!