In the latest picture I agree it does look a little more like yolk. I've had it before where all of the egg goo, poo and yolk stuck together like glue to the shell and ended up having to slowly with a wet rag wash off the extra excrement/goo so the yolk could fully absorb. Do you know what day the eggs were on when you found this little one? That would let us know how long it should ideally take to absorb the yolk sac. For example a duckling that hatches 2 days early vs. 1 day early will take an extra day or two to fully absorb the yolk. If you are keeping it in the incubator I use a warm damp wash cloth. If you're not then go with a dry one. If the little one does make it I would get it on some poultry cell or whatever supplement you use. I've had many assisted hatches due to the breed I hatch and every single one needed continued extra care for the first few days once moved to the brooder.