Yes, ferret lovers tend to be poop watchers.  We're either cleaning it up or examining its color and texture to monitor the health of our ferrets.  Here's a chart on the various color and consistencies that one may see and what it might mean.  This information was originally posted to the Ferret Mailing List by Dr. Bruce Williams, noted veterinary pathologist and ferret expert.

• Green poop - a very non-specific sign - it just means that food is moving through too fast. The normal brown color seen in feces is the end product of breakdown of old red blood cells. The pigment goes through a green stage called biliverdin, before it becomes brown (called stercobilin). So if it is going through at an accelerated rate, it never breaks all the way down, and has a green color to it.  Anything that accelerates passage of food or causes diarrhea can result in green color - ECE, rapid food changes, lymphoma, just about anything.
• Black tarry poop - Very suggestive of gastric bleeding and usually associated with gastric ulcers. You have to have significant bleeding in the stomach for the feces to turn black. The black color is the result of digestion of blood, which usually only occurs in the stomach.
• Bloody poop - If you see frank blood in the poop - it is usually either from the large bowel or rectum ( if seen in small amounts) - of if there is a lot of blood, it could come from the entire length of the GI tract.  Massive hemorrhage is seen either from severe gastric bleeds or shock in ferrets, and as one might imagine, is a really bad sign.
• Birdseed poop - Generally a sign of maldigestion or malabsorption. Also non-specific, it can be seen with any disease that severely affects the small intestine. Most commonly seen with ECE, the individual seeds are usually undigested fat and starch complexes. When you see this, you should consider removing a ferret from kibble and going to a bland, easily digested supplement for a while.
• Pencil-lead thin stools - Think partial obstruction - usually a foreign body.