I always hatch brown eggs & have tried to candle but never can see anything. So, I just wait. I've got 48 eggs in the bator now & its day 13. Eight more days & I'll find out whats what. I do hope they all hatch because I have them sold already.
I usually only candle on day 10. If the eggs are really dark-shelled and I can't see anything on d10, I will sometimes try again around d14, but I really dislike handling them a lot so I try to leave them alone as much as possible.