Color. What color do you expect it to be? Normally, it is dark because of the presence of bilirubin biproduct, stercobilin. I'd be concerned if it were "light", it then may signify a problem with your bile excretion. On the other hand, if it is liquid and black it may signal bleeding from your gastrointestinal tract that needs to be promptly evaluated.
Poop varies. Without an exam, I can only give general information, and stool can be very very dark if there is iron in it (often from bleeding somewhere, but can just be from vitamins or foods).
Color change. The stool can go through color changes on a daily basis, mainly dependent on the foods that you eat. If the stool color is consistently an abnormal color, independent of your diet, then follow with a doctor for further evaluation. It could be the sign of a malabsorption issue.