Are they pipped as well? Steam up your bathroom really good and candle them if you're worried and they're not pipped. If they're pipped, you can chip away a little tiny bit of shell and use a flashlight to peek inside. Usually discolored spots mean either that the baby is in the air cell or that they've passed.
I'm an experienced hatcher and I lost two ducklings this recent hatch that pipped, turned and suffocated themselves. Sometimes they just don't make it even if they are perfectly formed.
As a side note, I usually know by the end of day 27 whether or not the hatch is finished. After the second one suffocated itself last night, I candled the rest and they were done for. But I have 8 adorable babies in the brooder.