Ah, well, you don't have to get all scientific about it, chicken liver is pretty cheap, mostly readily available, and you wouldn't want to feed more than about 1/2 a one a day. I would just wait until the color has noticeably dropped off, then start feeding the liver for a few weeks and subjectively see if it gets better before I would embark on a 2 year science project... If it does, I would probably just do a maintenance course of a once or twice a week treat. Liver is actually so high in certain vitamins that it is possible to develop excessive levels of Vitamin A from overeating it, but that would take a lot of liver and wouldn't happen in the states, since organ meats are not very popular here.