I agree with the others. I think you may want to continue on for a few more days. I would, just because I want to get my intestines squeaky clean. Plus if you are feeling good, why not?
Black, however, usually means blood, so keep an eye on it. Maybe you had a clot in there that loosened up from a long time ago. Hopefully it doesn't continue to be black. In any case, check and see if your tounge has gone back to a clear pink. That's usually the indicator that you've gotten rid of most of your toxins. If it's still white, definitely stay on it.