Did-coloration in sohal tang

[Duality]

I was wondering if anyone would know why my sohal is loosing color and getting blotchy in his body right before his tail
Here's a few shoots I could get

Here's one for fun

Kisses anyone.
This blotchiness comes and goes. It's been happening for a few years now. Could it be a disease or fungus.

 

[Dmorty217]

My first thought was injury, but it's hard to tell for certain. Looks to not be irritated like I would suspect

 

[fishpureluck]

I can't see the pics, but when a few of my tangs aren't happy, they lose color and get black blotchy. Then they are happy and back to normal. Mostly if I'm working in the tank or when I add new fish.

 

[Duality]

The first 3 pics are probably the best. See how the black in the strips r yellow right in front of his spike. That's about it in the dis-coloration.