Long term Velvet infection + Treatment complications. Any help?

[DoctorWhoLuver]

The blue and green on his tail is iridescence. Bettas have been known to change colors. Velvet is very prominent, and when you look with the betta facing you, you can actually see a dust-like substance poking from the fish's sides. I have had two fish with velvet and both survived. Velvet is easily treated and will not last more than a week, usually. This is a very fast acting disease.

[MDS91]

Is there any way to definitively test whether velvet is present or not? Some kind of aquarium vet or something that can test water samples or skin swabs, if that's even a thing for fish? Given what I've seen, I have a hard time believing that it's not some form of velvet, but if there's a way to know for certain, I'll gladly look into it. As bad as I'd feel if I was in fact treating him for nothing, I'd be extremely relieved, but from what I've seen consistently over a long time, I am pretty sure that's what it is.

[MDS91]

Forget the blue for now, He initially had a pretty classic case of velvet, of that I am 110% certain. What makes me so sure he had velvet at least up until the flubendazole was appearance of the 'gold' on fins, the top one in particular. It appeared to have a very grainy(as in tv grainy) appearance up close, and during peroxide treatments, would noticeably fizz/melt/disappear in small patches nearest the drop of peroxide, revealing seemingly normal colored fin tissue beneath, and the fish seemed happier after the first few peroxide treatments as if they were helping. Gently rubbing his top fin with a peroxide soaked q tip (underwater, of course) seemed to have a similar noticeable effect. In both cases, by the next day any 'holes' made would be back to golden. As far as I know, which is admittedly not much on this, but I don't think natural iridescence would come off or behave like that. Could it?