@thorninmud is correct. Though I should also note only coral that contains a calcium carbonate skeleton will be able to be saved in this manner. All other non sclerite coral will simply melt away to nothing once it dies.
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@thorninmud There is plenty of live coral that is white. Its just non photosynthetic. The color in which coral displays is from the zooxanthellae algae it symbiotically hosts within its body. There are many species however that live at depths in which the sunlight can not penetrate so the animal depends on micro-organisms in the water column that they catch with nematocytes at the end of their tentacles.
I really hope your not taking coral out of the ocean though or supporting such a thing. Its one thing to take a piece thats already completely dead(though even these provide structure for the next generation to grow) its another to take live colonies just for ornamental purposes which is often the case.