UPDATE: I have the same problem as the OP! Did you ever find a solution?
Mine was shipped, acclimated, and looked like the picture I posted above for months...then out of nowhere it lost all its color. All my other SPS have beautiful color, and fast growth. This guys still encrusting and getting larger, just no color, almost a drab grey. I tried dipping twice to rule out pests. My parameters are identical to the ones I posted in Nov, Im stable everywhere.
Any ideas or suggestions?