Actually I keep two croceas under PCs in my nano cube. They are on the rocks about halfway up the tank and seem to be doing fine. One has been in there since august. I know everyone states that they need MH lighting, but I have also read that that topic is still under debate.
Alyssia, T5s are fluorescent tubes that are thinner (I believe) than standard tubes, but are more intense and higher wattage. Four footers I believe are 110w. They require a different ballast too since they are higher wattage. I don't have any but have read a little about them in catalogs and such.
As for colors, I find that my clams are actually iridescent and the color depends on the angle you view them from.
Oh and back to my lighting, I have been told by a lfs guy that my clam will need more light later on. Not so much a problem as eventually I am switching to MH over my 75-soon-to-be-110 gal tank. So don't start screaming and flaming.