Tagging along on this as mine turned brown too about 2 years ago and haven't been able to get them to turn green again.
Water params: NO3 = 0.07, PO4 = 0, Alk = 9 dKH, Ca = 420 pH = 8.0, Temp = 79.9, sal. = 1.026
T5HO: 4X24 watt; 2 ATI blue+, 1 ATI Aquablue Special, 1 UVL Actinic white @ 12 hours dusk/dawn and 5 hours daylight (AquaticLife default timer settings and bulbs are new and changed out every 12 months).
Doesn't matter where they are placed in the aquarium, changing the water flow doesn't effect them nor does feeding.  I've just resigned myself to having brown star polyps.  Though there is some green left in some spots.