dark streak in stool

Hi everyone.  Im a 27 year old male w a history of gerd and hemmorhoids.  Lately, Ive been noticing that parts of my stool are different colors.  For example, i had a dark stream down the side of my stool.  I have guaiaced it several times ( i have strips and reagent at home) and its only positive whenever i have an active bleeding hemmorhoid.  It doesnt really look like blood, but its darker then the rest of the stool.  It doesnt happen with every bowel movement.  I have a family history of colon CA.  should i be concerned?  any idea what this could be?
thank you

[boron]

Blood from color (cancer) would be red in any case. Gut blood has black color only, if it originates from the gaster or esophagus (in any case it has to go through the gaster, where acid changes it into black). You may want to check, if your test can detect this acidic blood. If you can't get rid of a feeling it's blood, go to some lab. It may be from polyps, or from crohn's disease or...27 y. is young age for colon CA though (except if it appeared at young ages in your family).

Other causes of black stool:
- Pepto.Bismol
- iron supplemments
- bluberries, raspberries
- maybe bacterial or candida overgrowth, but this would cause bloating, diarrhea or so.

[JJJ78]

The thing that confuses me is that its only on one side.  The whole stool is never entirely discolored, and its usually only on one piece.  I have parts of my stool that are darker then others, but not the whole thing.  If i use something to spread it, the water does not turn bloody, so it really doesnt look like blood.  

[boron]

Have you maybe add some new food (vegetable, tea) in your diet "lately" ?

OK, one rare possibility: In Meckel's diverticulum (inborn defect), a small part of distal  small intestine is replaced by gastric mucosa, which may secrete acid and cause ulceration and bleeding. This blood would be black. Since this mucosa is like in the pouch on one side, it is just normal, if the stool is black only on one side. This would go with middle right abdominal pain (not necessary). There is not always so much mixing inside the bowel, as you might think.

Another: if you have inflammed diverticles (diverticulitis) in the last part of the colon, stool can be trapped there, inflammation can cause bleeding or not, anyway, some old stool can be dark.

What to do:
1. Is it blood or not (reliable lab test). Before the test you might want to esxclude some suspicious food from the diet. Aspirins may cause gastric bleeding also.
2. well, think from there

[JJJ78]

Boron:  I have guaiaced the sample, and its only positive when i also have blood on the tissue paper from hemmorhoids.  I dont think its blood, just wondering what else can cause one side of it to be completely different color then the rest.  I dont eat any unusual foods, dont take NSAIDS.  I do take nexium for gerd.