that doesnt look terrible to me, and black on the exhaust tip is normal, especially on higher mileage (idk how many miles on your truck) vehicles, if you are worried about it change the O2 sensor with a OEM plug and play model, DO NOT CUT/SOLDER to put a new one it, you always want a plug in part for something like this so that you can easily change it if needed.

 

I was talking about the pre-CAT (the one BEFORE the CAT). Now understanding that it might have been the rear (which I still don't know). If the light comes back on I would replace the pre-CAT as that is Bank 1.