i have a tang that looked 100x worse than your regal did, when i got started i did the same thing and moved a full setup from one place to mine and swapped everything over, biggest thing to remember is those fish need oxygen and also heat. i put all fish in one tote with a heater and a battery bubbler for over a day and they all loved it. one thing that looking back on the last year and a half of this hobby is that everything takes time and anything rushed results in failure more often than not. Its taken a full year now of good water conditions for me to be able to keep SPS and that's only happened in the last month or two. Back on topic, tangs loose their color like that if they aren't being fed a proper diet. get some nori or herbivore pellets into it and it will get its color back and look great minus a bit of scaring. mine got its color back in less than 2 weeks of having the right food.