I agree that it's a BTA and for whatever reason, it's lacking zooxanthellae.
That said, offering live zooxanthellae may help. There is a product called PhycoPure Zooxanthellae and Live Aquaria is currently running a sale on it. It's not a magic cure but IMO it's close when offered to a relatively healthy zooxanthellae-challenged anemone. The fact that your nem continues to eat is half the battle. Kudos to you for keeping the animal in such good condition for so long without the help of zooxanthellae. Normally when a nem bleaches, at least some zooxanthellae remains and eventually reproduces to replace what was lost. But IMO, your anemone has no zooxanthellae left whatsoever. The faint color you see is mere pigment not to be confused with zooxanthellae. Therefore, unless the nem gets some donor zooxanthellae, it will remain transluscent and dependent soley upon you for nutrition which is not the optimal approach to anemone keeping. An opaque BTA could also serve as a passive zooxanthellae donor as could some coral- the closer the proximity the better providing allopathy isn't an issue.
Regarding your lighting. I believe it's Marine Double Bright? That fixture may or may not provide enough PAR to keep a BTAs zooxanthellae intact. I'm not going to say it absolutely won't but I will say I suspect it won't. The fact that the nem has worked it's way to the very top of the tank is a clue it may not. For what it's worth, my BTA's seek PAR in the 150-200 range and in the world of reef-lighting, that's not much. BTA's have minimal lighting needs in comparison to other anemone species. I recommend learning what the PAR capabilities are at certain depths for that particular fixture, which I don't believe was manufactured for reef purposes.