Then, I would be looking into coffee enemas and digestive aids. Both of those have made my stools much darker. I know how it feels to be worried with the cromatic abnormalities of feces.
Also, taurine its just one element in the liver pathways, you could try adding more of them, but sincerely that route its stupid compared with the other possibilities.
Lastly, why dont looking into liver flushing? Its theorically the best way to ensure bile flow isnt it. I am gonna do one serious the next week. We just need that bile flowing.