First of all
the discolored goldfish doesn't seem to be diseased from the photograph.
Especially if the discolored area is not raised above the normal skin.
Gold fish often change color with age.
I would'nt worry too much about it.
If you'd like you can put him in a bucket and bring him down the store and I can take a closer look.
Second item
2 replies posted to your inquiry were not only stupid and rude
one of the morons SIGNED MY NAME, and I not amused.
Rest assured that if the REAL Ned Bowers gives you a flip answer to your questions it will be funny, informative and not Junior High.
Regards
Ned 800 683 5165 cichfish@aol.com