Hello No...
Looks like a small change in the pigment. Most would call it a freckle. It doesn't look serious. Goldfish can and do change color as they age. What's your water change routine? I keep quite a few fancy Goldfish and change half or more of the tank water weekly and use a teaspoon or so of standard aquarium salt in every 5 gallons of replacement water. Keeping the water clean will discourage the growth of any parasite or virus. If your fish is acting and eating normally, I wouldn't worry about it. Just keep the water clean and consider adding a little aquarium salt.
B