Zoanthids will change color based on the tank conditions. Unless your conditions are literally exactly like those of your supplier the zoos will change color to some degree. The same is true for any coral. Unfortunately we don't have an understanding as to why all these changes occur. The best thing you can do is call your vendor and see if they'll tell you their system parameters (lighting, Ca, nitrates, etc) and try and match theirs. Even that may not work though.