ok I can understand that you had the water tested but I (and everyone else) need numbers to Identify potential problems. the LFS Idea and my idea of fine may be totally different (probably are) numbers would help a lot if you can remember the results of the tests.
the things we need to know are SG level or salinity wichever you prefer, temperature, calcium, alk, ph, ammonia, nitrite, nitrate.
I dont think depriving the coral of proper lighting is going to help it in any way, only hurt it as for those three days it couldnt gain energy through photosynthesis, so it may have weakened it more.
Usually when corals darken its a sign that they are growing more symbiotic algae for photosynthesis, potentially due to lower lighting than they may be used to. about all I can suggest is leave it be and hopefully it recovers as I know almost nothing about the conditions. sorry I couldnt be more helpfull.