If you were producing sufficient bile in my opinion the stools would be dark brown.
I once had a conversation with a Dr. about what slate colored stools meant. He said grey but my idea was that they were tan. When I'm producing enough bile my stools are a darker brown than when my bile system is congested. There are certain bacteria that eat bile and if you carry these organisms they could be using up the bile you produce in the bile system and in the intestine. Do a search for 'bile metabolism bacteria'.