Answer:
What measures out time. Until in time all is smashed to it?
I am a box that holds keys without locks, yet they can unlock your soul.
In the night a mountain, in the morning a meadow.
Only one color, but not one size. Stuck at the bottom, yet easily flies. Present in sun, but not in rain. Doing no harm, and feeling no pain.
Reaching stiffly for the sky, I bare my fingers when its cold. In warmth I wear an emerald glove and in between I dress in gold.
I am rarely touched but often held. If you are smart you'll use me well. What am I?