Well first of all you could buy some nice corals with 50 watts of light over that tank.
BUT your live rock is technically alive. If it's any color other than white then more than likely some type of algae, bacteria, whatever is growing on it. You should see little things sprouted off of the rock. Best place to see that is the underside of rocks. Back to the white thing. If your rock is completely white then you need new live rock. Do you have anything else in the tank. If you do then your white rock will eventually, after a long time, turn back into live rock, i think.....