Normally, a fresh egg has a yellow yolk, a layer of thick albumen (egg white) surrounding the yolk, and a thinner layer of albumen surrounding that. You can see when you crack an egg open that there are the two layers of egg white are actually quite different.
The yolk is tethered in place on opposite sides by two chalazae, short white twisted strands that anchor the yolk to the white. All gets, whether fertilised or not have the chalazae.
Fertile eggs are edible. In fact, some people consider fertile eggs more nutritious than infertile eggs, but this is an old-wives tale – scientific research does not confirm this. Fresh fertile eggs will not have embryos in them. Embryos do not begin to develop until the eggs are being incubated under the hen.
The egg yolk may be any shade from yellow to orange, and depends on the diet of the chook. The colour is usually consistent if hens are fed only one type of feed, but foraging hens and those fed kitchen scraps will often produce a variety of yolk colours. As long as you know that the chook has received a healthy diet any yolk colour is OK. Obviously by keeping your own chickens you will always know how the birds have been kept.
The egg yolk or egg white may have specks in it. These “blood spots” and “meat spots” are harmless bits of tissue and are allowed in commercial Grade B eggs. If they look unappealing, the spots can be removed before cooking.
An eggshell has a protective coating that prevents bacteria from entering the egg. To retain this coating, eggs should not be washed until just before use. Sometimes eggs are soiled with blood from minor tissue damage or mud or feces from the nest box. This can be wiped off carefully; the shell should be thoroughly dried.
If you are not sure how old an egg is, you can put it in water. The freshest eggs will remain at the bottom of the container, while old eggs will float. Floaters should either be discarded or opened far from your nose.