Try around day 12. I can't tell anything at day 7 either. Any dark egg is going to have that problem.
I'm trying to candle welsummer eggs. I am not able to get through the shell with my candler and it is a good on from what I have thought. Does anyone have any other methods of candling the eggs? I just end up candling them at day 18. If I cannot see through it then it is a keeper and if I can see through it is a clear. I just cannot see anything at day 7.