It is normal for the yes go black after death. Usually, the eyes contain blood vessels. When one of those veins pop for a alive person, it will make your eyes appear red. But if this happen to a dead person, it is probably appear black because the blood gets old and the blood turn back. If those blood in those tiny veins turns back and the tiny veins cover your eyes, it is of course make the eyes appear black.
Yes, I agree. This is kind horrible to answer. But I guess I can still help you. When you are alive, your eyes have blood veins under the skin so your eyes will look red sometimes. No matter when you are ill or when you get an eye infection, people will just see your red eyes, which is also very normal. However, after you die, your blood will stop flowing. Do you know that dead blood will turn black? That is, dead blood is black while fresh blood is red. I hope this is clear for you.
The change in eye colour that you can see in the eyes of dead people is due to opacity of the cornea, aqueous humour and lense brought about by lack of oxygen. Once a person dies, they stop producing tears and blinking, and blood circulation ceases. The cornea must be moist in order that oxygen may be absorbed.
After death, the cornea loses its glistening appearance and becomes dull & opaque. The eyelids usually close after death due to primary flaccidity of the muscles, but the flaccid muscles usually fail to produce complete exposed, a film of cell debris & mucus forms 2 yellow triangles on the sclera, which become reddish brown and then black, and dust settles steadily. Hope this helpful.