First of all if your going to keep an anemone then purchase the best lighitng that you can afford. In the case of the BTA then you should have at least 260 watts of lets say VHO over a 50 gallon tank.
If you see a white BTA then steer clear, white anemonies have suffered bleaching and are likely unhealthy.
What is anemone ‘bleaching’?
All healthy anemones have a population of zooxanthellae in their body tissues that helps provide nutrients to the host anemone. This algae population is brown in color, and all healthy anemones will have an underlying color tone of light to dark brown depending upon the intensity of lighting under which they are kept, and the size of their zooxanthellae population. In cases of stress or poor water conditions, the zooxanthellae population in an anemone can die or be expelled. This condition is called “bleaching” since a healthy, dark colored anemone can become light and pale overnight. Bleached anemones are white or translucent in color, and lack the noticeable brown undercoloring of healthy anemones. The lack of zooxanthellae puts an anemone at significant health risk, since it no longer has a substantial source of nutrients. However, even badly stressed and bleached anemones can recover if placed in a stable, healthy environment. Daily feedings and appropriate light conditions will help the animal to rebuild its zooxanthellae population and reacquire its normal tan/brownish color over time. This process may take a while – three months is not unusual.