I have green BTA's and 2 black clowns in my 40gal reef. It took almost 4 months for them to figure out what the BTA was, and now they go in and out but they dont stay with it at all times, they do enjoy swimming around the tank.
My other tank with a green BTA and 2 orange clowns, nothing happens, they couldnt care less if the BTA is there or not, instead they just like to attack me when I need to get my arm in there to move a coral or rock...
Tank raised clowns it hit or miss if they host it or not, I got my black ones to start hosting by taping a picture of other black clowns inside a BTA to the side of my tank (yes it sounds silly but I did it) and I also started to feed the clowns near the BTA so they would get used to them being so close, and once I used the picture it took them only 3 or 4 days to start hosting the nem all the time.
35gal Reef, 20gal Sump--2 years, 3 months--Shut Down
If you can't fix it with a hammer, you have an electrical problem!