Zoanthellae is never white. Companies leave anemone in the dark to make them turn white. It probably started as unattractive color. Or collected poorly. When under stress or lack of light the anemone will lose its zoanthellae and turn white. Then they can no longer feed them self off photosynthesis. When that happens they shriek from light and spill their guts. Some research on the subject can provide more insight than can recall.