The Formulary's amidol is always dark grey, but it works just fine. I usually have a few small particles that do not dissolve, and I simply strain them out. The amidol I used to get from Bryant Labs was a white crystalline powder (well, maybe off white), and it dissolved very easily and left no residue. Amidol crystals are very light, so it seems to take a lot. My knowledge of chemistry is limited, but perhaps someone could tell us if there are aren't several ways to make amidol that result in different grades.
Someone referenced a thread on Michael Smith's site. I believe he said something like he has some very old amidol (40 or 50 years old) that is quite black but still works fine.