the color of blood is determined by where in the digestive system the bleeding is occurring. For example if the bleeding is in the duodenum (1st part of small intestine) the stools will be black because the blood is digested and will turn black. If the bleeding is in the lower part of the colon or near the rectum the stools will have bright red blood in them. Also the reverse is true if the dog is vomiting blood that has been in the stomach, it will look like coffee grounds because it has started to break down from the HCl in the stomach, but if the dog is vomiting and then you see red blood it could be from a broken blood vessel in the esophagus from violent vomiting. The meds could be the cause, especially Rimadyl, if Zoe isn't eating much. Sorry if this sounds too technical but the same is true for humans and I'm a nurse
. Good luck with Zoe.