Green Birdsnest polyps white??

[Jessie55]

When i got my frag a few months back the polyps were green as they should be but now they all are almost completely white i don't understand why. The polyps are always extended and the frag is growing like mad i can see the growth everyday. Too much light?? It is under 6 ati t5's and is placed about 8 inches down from the surface of the water.