platy appearance

Question
i have a sunset platy and i noticed that he has some grey now on top of this body..looks almost like he has been dusted with soot, has an almost grey dusty appearance.  he is eating and swimming fine.  can you tell me if this is some kind of infection?  my guppies, neons and gourami are all fine.

Answer
Hi Susan:  fish change color for a variety of reasons.  One of the reasons is diet and another is aggression.  I would add some aquarium salt to the tank and keep your eye on him.  It could be a disease but at this point it would be difficult to diagnose him and medicating blindly can cause more problems then you started with.  Keep me posted.  In the meantime offer him/her some brine shrimp and make sure he/she is eating and pooping.  dave