Black, undigested vegetables in stool

Hi,

I've been having stomach issues for a while now (I have another question about those already posted) and, as a result, have been taking special notice of my stool.

I ate some pizza which had capsicum and white onion on it last night, and this morning I noticed that the pieces of capsicum and onion came out the same shape they went in (the capsicum was maybe slightly softer) and black.
The capsicum pieces were pitch black, and the onion pieces were a sort of patchy black.

Is this normal? A friend suggested that they could possibly be getting coloured by blood in the digestive track, but I'm not sure that could happen, could it? I know that is sometimes the case in black stool, but the actual stool is just dark, not black, and the bloody stool I've had lately is (warning - gross) red blood mixed with mucus. Although I have also noticed some black specks.

I'm just wondering if maybe vegetables just do this anyway (I noticed something similar when I had broccoli), or if I should be concered? I haven't been able to compare much as I haven't been eating a lot of veges as they seem to cause stomach and gut pain.

Any help would be appreciated.
Thank you!

[jennerfennerbenner]

I have ibs and this happens to me all the time especially lettuce