Sail Fin facial pigmentation changing to black in color

[AwwNuts]

Not sure if i have this in the right section but i'm giving it a shot.

have you guys ever seen a sail fin change pigmentation. Within this week i would say starting on 9/24 my sail fin facial pigmentation has been changing to a black color.

before pic

now(sorry for the crappy pics my cell sucked this time, and this tang loves to swim in the 125 gal tank

 

[AwwNuts]

The day before it started i don't know if this has some part in it but my wife was being a of help in cleaning up some of the salt creep on the top glass lids. Well some salt flakes fell in while she was cleaning and this tang was eating them as they were floating down.

the next day half of his face was starting to turn black and now well his entire face is black and its starting to extend to his body.

Nothing has changed with the fish. Healthy as ever, swimming like its the olympics 24/7 and eating like a pig lol.

wonder if he will morph or change back lol.

Just thought i get some imput if anyone has gone thru this