Coralline has to be introduced to your tank by an outside source ie- Live rock. If the lr only has 1 color on it, chances are that's the only one that will flourish. If you buy small amounts of LR, each piece bearing a different color then... well you know. Or a much cheaper solution, would be to go to your LFS and find snails with it on their shell. That also helps speed up the spreading, because they seed your tank all over.
If you already have it in your tank, then keep your calcium and dkh balanced and in check as Footbag suggests. Personally, I used Coral-Vital by Ken Weiss to help mine along.