They are brown when they are stressed.
More then likely it is over feeding but don't feel bad as I still do the same after having a salt system for almost 3 yrs now and fresh for many before that. It is hard to get the correct amount of food right in the beginning as your stock is changing along with other factors like trying different foods. I have a large stock and still not quite sure how much food to put in. On normal days I feed twice, 3 pinches of pellets in the morning then I rotate 2 frozen cubes with pieces of nori mixed in and mysis with microvore in the evening. I also hang nori a couple times a week. I soak the frozen and mysis in lipids and garlic guard twice a week. I still get a small amount of diatoms on the sand so after cleaning I give a tiny bit less and see how long it takes to come back.
I managed to get a good pic of my Midas Blenny, its on my thread you can see the pink shade on his side. From what I have read they can come completely yellow or have a couple different sides to them like pink and blue.