There is one thing not mentioned yet here.... and that is coral species and/or origin. I know that many of us can look at a new coral shipment and tell which coral colors are going to hold in our tanks and which are doomed to quickly fade. Many of the Fiji corals that come out of the box with bright yellow, pink, baby blue, etc. will only become less vibrant in our systems; yet, I have had tan/brown corals come in from Bali that turn into absolute jewels. I have a feeling that many of the Fiji corals are harvested from portions of the reef (namely, high light or absolutley pristine water parameters) that are impossible for us to replicate...so, the coral's color fades. I now only add corals to my system that I know will keep or improve in color....I've passed on many brilliantly colored corals on shipment day only to purchase the "brown turd". The wisdom of my choice is only apparent in a few months time. This comes from the experience of having utterly failed at being able to maintain the color of some of the brilliantly colored Fiji corals.
So, your inability to keep some of the brilliant colors may be more a result of being doomed from the start from a poor coral color choice. One way to be sure is to obtain frags from fellow reefers whose corals are holding their color...... it's this reason why the Oregon and Cali torts are so popular...these are corals that maintain their brilliant colors. It's an expensive speculative game to play when dealing with wild corals.