Answer:
What has a single eye but cannot see?
A nut cracker up in a tree.
What do you fill with empty hands?
They're up near the sky, on something very tall. Sometimes they die, only then do they fall.
It doesn't live within a house, nor does it live without. Most will use it when they come in, and again when they go out.
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.