Can stool appear black despite stopping iron supplements?

Hello doctor,

I have had iron deficiency anemia for three months. In short, my third CBC doctor said everything is going fine, and my hemoglobin level is increasing. I have also done another blood test, even if I have not used iron supplements for two days. My blood levels were still increasing; I asked the doctor about losing my appetite and if my iron deficiency was the cause of my stomach bleeding. And he said I had to have a coffee-like stool or vomit.

Later that day, when I woke up, my lower abdomen was gurgling so much (with no pain), and I went to the toilet; that was some liquidy stool (or tarry), and I had not used iron supplement for one, and half days though it was still black (One day ago, I only took 5 mg, and the other day when I check my CBC I did not take my iron supplements at all as I forgot to take me with them)

If I had gastrointestinal bleeding, would it show up in CBC? And how long does iron supplement stay in the body?

Is it normal for my stool colors to be black even though I have not taken them for a day?

Kindly advise.