So, Quasimodo is a Wal-Mart "rescue" who was doing really well. He was only slightly less active than my sister's fish, who is in picture perfect health. I don't think he will ever regain full color in his dorsal fin (has a black patch) or that his spine will ever look normal (hence his name).
I had hoped that his color and spine would improve, but I think he's as good as I can get him. I left him for 2 weeks in a 2.5 gallon tank after a 100% water change. This decision to leave him so long without a 50% change was based on previous parameter checks. I returned last night to a fish that was discolored (lost 50% color in fins and had patches of flesh colored scales) and had greenish-blue eyes. He obviously hadn't eaten much of the 10 day feeding pellet I had left for him. He was weak and barely ate. I immediately did a 100% water change and put some more food into his tank. I went to bed. The next morning, I awoke to a fully colored fish! The only sign left of his near demise was his obvious weight loss. I regret not taking pictures of him for you to see.
Needless to say, I should have checked his parameters and I'll not be leaving him again.
Anyway, I would like some facts, thoughts and opinions on color loss and gain. What causes it? What vitamins/minerals enhance color? Why were his eyes blue? What are some things that cause permanent color loss? I haven't seen anything on the forum to discuss this specifically, although it is a very common sign of illness.