Is this velvet disease?

my guppy which i have had in a 10 gal tank for a month now seems to be changing color somewhat. this color change has been happening only on his head, he is a blue delta guppy but towards his lower silver head its beginning to turn gold, kind of. he appears very healthy however, and not scratching himself at all. upon inspecting him with a flashlight the color has a shine to it, and it does not appear powdery at all, and it is all local to his head only, and i would figure if it was velvet the gold would show up all over his darker body. and with the amount of time his head has been turning i assume the other fish would have gotten it, but no others show symptoms. is it maybe poor water? or something else? or is it actually velvet?