Green Birdsnest lost colour, but not bleached

[Reefie]

I've had a Green Birdsnest frag for about 3 months now, and was experiencing good growth and polyp extension. I previously had 2 Hydor Koralia Nano powerheads for circulation, I just upgraded to a pair of the Tunze 6015's to improve flow. For some unknown reason, the Green Birdsnest polyps have lost all their colour and have gone white. It still has full polyp extension, just no colour. Everything else in the tank is doing well and has good growth and polyp extension.

Has anyone experienced this phenomena before? Will the colour come back?

I originally thought it was getting bleached, but it has been in the same spot for the whole 3 months. I've just moved it to the other side of the tank to see if it helps. It is still getting full polyp extension in it's new spot, but still no colour.

I'm running 2 Vertex Illumilux 12" LED modules (Marino Bianco) and 2 Ecoxotic Blue Stunners for moonlight.

Water parameters are good, as I do 25% water changes about twice a week and am experiencing good growth with all other corals.