I have had a yellow mimic tang for about a month. I just noticed that when you see him in the light it almost looks like he is getting blotched on his skin. They are like the yellow is fading in spots. At times it looks like it might be getting better and then it might look worse. I am feeding it seaweed selects. The pieces last several hours and I end up putting about two in for the day. I also feed flake food and some frozen food that I feed the other fish. I think he is getting enough greens but I don't know why his color is looking faded. By the way he has gained weight since I bought him.