What Causes Black Discolouration In Finger After Insertion Of Titanium Pin?

I had a fusion done several years ago on my left index finger. A titanium pin is still in the finger. It has tried to push its way out from time to time. But today my finger is discolored like a black where the point of the pin is. Should I be concert? It only stings if bumped but otherwise it doesn t hurt. Sharyn