Well it's definitely true some corals get their green on when put in a new system -- Although besides that, it's typically nutrient related, or an abundance of particular trace elements. Look at the red sea coral color kit, you'll see to bring out colors X, Y, or Z, you need to dose certain elements. Can't recall which particular element helps green pigment right now.. But that may be one of the first things to look at.
One other thing I see advised, and personally believe may be a good idea, is a series of larger water changes over the course of a week. Maybe 3 30% changes spaced over a week, possibly 4 over 1.5 weeks.
I've heard the series of water changes explained as a "reset", and I honestly think there may be something to that. Changing 10% of water weekly means 90% of your old water remains, and that 10% of new trace elements will continually get sucked up faster as the tank matures. Worst case scenario, it won't hurt.