Yellow Tang not looking good..

[roclimber]

Hi there, i purchased a yellow tank just about a month ago. Fish is doing fine ( although it has been hiding behind the rock most of the time but does come out and eat the seaweed and flakes ) so far.

Yesterday i was watching the fish and i noticed the skin has some sort of "rash" looking to it...when i looked closer, it's almost like orange in color above the eye as well as the rear part of the body ( close to the tail ).

Does anyone know whether it's some sort of disease? and what should i do?

thx in advance for any help or advice.