Answer:
A time when they're green. A time when they're brown. But both of these times, cause me to frown. But just in between, for a very short while. They're perfect and yellow. And cause me to smile.
Black we are and much admired. Many seek us if they are tired. We tire the horse, and comfort man, and turn White when we've fulfilled your plan.
What relies on columns but isn't a house, and asks for help but can't speak itself?
Surname of the pilot of the Millennium Falcon.
A dragon's tooth in a mortal's hand, I kill, I maim, I divide the land.
In birth I spring forth, in life I unfold. In death I wilt and die, but rebirth restores all.