I hate to disagree, especially since black edging usually screams fin rot. But I have a boy with similar colours, his fins and tail are rimmed in black, and it's natural colouring. Since it is so hard to tell feel free to use the salt treatment at a low dose, but what you really want to monitor is if the fin length is getting longer or shorter.
When my boys missing piece of fin grew back in it looked like the black edge was growing, only getting thicker. But the overall length of the fin was increasing, if that makes any sense.
He looks very handsome, I might have to steal him :D