Hello,
We purchased a juvenile Emperor Angel about 8 months ago, I think. Could have been sooner and could have been longer. But, anyway, he has changed from his juvenile coloration into an almost fully changed adult. He isn't fully changed over. The horizontel lines haven't fully developed and the portion around his "forehead" area is still a dirty white color that should be yellow as an adult. But, he's only about 5 inches so, he still has some growing to do. I really wouldn't recommend a large Angel for the size tank that you have listed in your profile though. They really do need a large volume of water to move around in. I'm sure we'll trade him in before he gets too large because I don't even think that a 125 is large enough. Oh yeah, and, make sure you provide a varied diet with frequent feedings of food containing sponge (like the frozen angel formula), as well as, a variety of flake food and some different types of meaty foods. Good luck. Hope this helps.