No, you're not crazy. The first time I ever saw my fish change colors, I thought something terrible had happened to them! I learned that fish have chromatophores or melanophores(?), let's go with 'pigment containing cells', that they can adjust when stressed (or not stressed). If I happen to walk into my dark living room at 2AM and turn on the lights, usually all of my fish will be colorless. Within 15 minutes, they get their color mostly back. My normally vibrantly blue and red betta fish goes all brown if he's very stressed. Since your (amazingly beautiful) angelfish has just been moved into a whole new home, naturally he's going to be a little stressed especially if someone he has not yet learned to associate with food approaches the tank. I wouldn't worry about it.