If I get one that's transparent already, I try to feed a piece of shrimp 2-3 a week. Gotta provide them with a food source until the can get their zoox back. I hear some ppl say that it takes them to much more energy to digest it vs letting them eat something but this is what I've been doing and it seems to work for me. I will say I have noticed that they don't always get their zoox back at the same rate. The last 2x BTAs I got about 4 months ago both came in very transparent (they are clones). One got it's color back within 2 months or so and has out grown the other one and as recently split. The other is still transparent and while it is bigger then when I got it, it's nowhere near as large as the bta that colored up. It's slowly getting it's pigment back but it's taking a lot longer. Both are on same feeding schedule in the same system. In short, try feeding it, keeping the water clean and maybe turning up the lights a bit.