Not sure on the iodine. I know that the nepthea are being kept with corals being grown out. The tanks have regular waterchanges and get heavy trace element supplements as well as amino acids and iodine dosing. And the tank have their trace elements monitored quite regularly to make sure everything is where it should be.
I think it's safe to say the Nepthea here in the states is getting Iodine available in similar proportions to Natural Sea Water. But if they were raising the iodine levels in Japan then that could be it as well.
Of course I have seen many Japanese Aquariums which use spotlights of different colors to highligh corals in a tank. So perhaps this flesh colored coral when put in front of a red spot light makes it look pink? Just another hypothetical speculation
Dave B