Purple tangs mouth turned white?

[Gtinnel]

My purple tangs mouth is white. It was not like that earlier today. The only thing that changed was I added a one spot foxface to the tank from quarantine a few hours ago. I noticed the color change after the foxface and the tang both ate nori from a veggie clip at the same time. It is not fuzzy like some kind of bacterial infection and the lack of pigment doesn't go too far up the face or on the lateral line like you'd expect to see with HLLE. He is still eating and acting normal. Can a purple tang change the pigmentation on their face to make it look like this, or is possible he was stung by the foxface while eating? I'm not sure what it looks like when a foxface stings another fish.
I'll attach a picture but it's not very good. I'm horrible at taking pictures inside the aquarium and after multiple tries this is the best I could get.

 

[JGT]

Thinking along with nori, he sampled the foxface’s spines which is venomous.

 

[Gtinnel]

Thinking along with nori, he sampled the foxface’s spines which is venomous.

I noticed he quickly darted away from the nori at one point. If he was stung will that heal without issue, assuming there isn't a secondary infection? I guess the good news is my qt/hospital tank is now empty LOL.

 

[JGT]

It should, provided it doesn’t become infected. I’d just keep an eye on it .

 

[Gtinnel]

Just a little update for anyone who sees this thread in the future. Within these few short hours the purple tangs mouth has already returned to almost normal.
Again sorry for the awful pic but you can see his snout sticking out from the shadow of that rock overhang.

 

[Garf]

Just a little update for anyone who sees this post in the future. Within these few short hours the purple tangs mouth has already returned to almost normal.
Again sorry for the awful pic but you can see his snout sticking out from the shadow of that rock overhang.

They only mess with a rabbit Once or twice before they learn.

 

[Gtinnel]

They only mess with a rabbit Once or twice before they learn.

I never saw the purple tang show any aggression to the foxface, which I was a little worried about because the purple is the "ruler" of the tank. Ironically it's my melanarus wrasse that will occasionally dart at the foxface. I guess if it gets too bad the melanarus will be taught a lesson.