Egg candling.... I always candled twice. Once at 7-10 days to kick out total "duds, not fertile.... then at 15-18 days as a recheck, pre-lockdown for hatching.
Dark and green tinted eggs are harder to tell. I have never had a "too bright" bulb to candle with. The room has to be DARK.... and the slot or hole the eggs are held against has to basically be covered by the egg to direct the light through the egg.
If the veins look like "veins" with no blurred edges then they are viable. Most embryonic deaths of eggs are in the 10-15 day range. That is mostly when you will see the blood ring very clearly. Before 10 days, mostly the egg just doesn't start to develop or just starts and has a very small hazy blood ring. There is small movement of the veins and the darker the shell, the harder it is to see the movement of the veins. If you ever have a chance to set a couple of white shelled eggs, and see the veins, you will really see the movement.
Do not over handle the eggs. Too much, especially too rough, will cause the veins to rupture, especially early on.
By 2 weeks, the eggs will be very much more "solid looking" with the developing chick. There will be some movement but the chick is filling up the space quickly.
Look up egg candling on the internet. I think that BYC has a pretty decent chart of progress from start to finish.
If you see veins, then leave them to develop. I have only had 2 or 3 eggs burst in the incubator over the 50+ years... mostly they just are duds, handle carefully when you take them out to dispose of.
Sounds like your eggs are doing good.
