Uncured = liverock that has die-off from shipping or otherwise being removed from the water. Easily detected by the smell. It STINKS!
Cured = liverock that has no die-off remaining. Smells earthy, but not offensive.
Uncured liverock will produce ammonia when you put it in your tank and should never be added to an existing tank. Any liverock you get, ANY, should be re-cured before adding it to a tank with fish and inverts. Once a piece of liverock is removed from water, it imediately begins to dry out and with that, die-off begins.
The loss of color is probably due to lighting. The coraline algae (the purple stuff) requires moderate lighting or else it will turn white or flake off. The rock is still 100% functional, just not very pretty.
