(Concern) After nerve treatment

I received root canal treatment slightly closer to the front teeth than the molars.

They have placed two and put fake teeth (?) on it!!

But recently I found that the part of my original tooth underneath the fake tooth has turned dark.ㅠㅠ

Is it just because there's no nerve that it appears that way??

Or could there be another problem?ㅠㅠ

I hope I never have to go to the dentist again after suffering so much during root canal treatmentㅠㅠ