Sometime this happens if the hen has had a fright, or somtimes in free range supermarket eggs, when hens roam with cocks the egg can be fertalized and you can see the developing chick. which is why i just keep hens.
If the inside of your mouth turns black, it would be worth it to pay a visit to your dentist. It could be something harmless like a blood vessel, or it could be an amalgam tattoo or precancerous spots.
Liver spots
by black spots on a white dog
black
its a live disease
black
Because people refer to them as black and whites. so what other color would they paint them?
The Speckled King snake is a black snake with yellow or orange spots speckled over it's body. Another black snake with yellow spots would be Baby Eastern Black King Snake. Both are completely black with yellow speckles.
The inside of an eggshell can have calcium deposits. This would form between the hard shell and the outer membrane on the inner shell. It is just a nutritional deficiency and will not affect the taste of the egg.
Those small black spots are normal, so don't worry! However, if these are lumpy then call up your vet to make an appointment.
Culture
If you are talking about the yellow stuff, it is called the yolk.