Manny of my ducks lay green eggs. There ausy spots.. Not sure how they compare to green chicken eggs though. I use a pitch black closet . i do not always see a red colored veins but you can still tell if it is a vein from dark shell lines by watching it as you move the egg around . i use a small 3 led light flash light not sure of how many candle power it has .but its very bright i make sure batteries are new. And you see on older embryos the darker shadow . when you candle a newly laid egg you cant even see the yoke . so you know it fairly easy to tell you have a live embryo latter after 5 or 6 days. I do not rush i look the egg over real well from all
Angles. A full minute seems like a lot longer than it realy is .