I believe the colors change depending on mood. My Dogface is a brownish-white, and the color fluctuates sometimes to all brown and sometimes to white. Sometimes I noticed he turns whitish when he is closer to the sand.
Just make sure you Dogface is happy and his needs are taken care of. Keep him on a varied diet. While mine loves any prepare frozen food, he also loves to eat seaweed. When I put in a clip for the other fish, my Dogface wants in on the action also and eats quite a bit of that as well. Sometimes he gets it stuck between his teeth, and it's fun watching him trying to get it out.