The black specks really could be anything... all sorts of changes take place in there with digestion. If you look around in different photos, they're in almost every enema photo. I wouldn't stress yourself out over it.
I'm not sure about diet after enemas, but I think you're supposed to drink more fluids like gatorade, juice, broth etc. to replace electrolytes.. maybe even take some magnesium.
I find when I hit the enemas too hard, my muscles get jumpy.