It's the light gray area at the base of his tail that I'm referring to. Maybe it's just the way he's marked, but I think that used to be solid black.
Oh, and if RSFish is reading this, I think this is the fish I got from him that he said was kind of a miracle fish. Something about him jumping out of a tank and landing on the ground or concrete or something. Said he should have died twice, but came around both times. Quite the fighter, so I'm hoping he is and will be alright. As I said, I noticed a small spot last fall, and now it seems there are 3 small pots. Maybe it's missing scales, maybe it's something else. Hopefully someone will check it out and let me know if they know. He seems fine otherwise, swims and feeds (when I fed) and acts normal. Just was worried since I mentioned he did him best "Shamu Sea World" act jumping out of the water 2 weekends ago, and someone mentioned her may be trying to rub or have a parasite! Then with the one baby koi dying ... made me start looking ultra close!