Answer:
Thirty white horses on a red hill, first they champ, then they stamp, then they stand still.
Sleeping during the day, I hide away. Watchful through the night, I open at dawn's light. But only for the briefest time, do I shine. And then I hide away. And sleep through the day.
What's black when you get it, red when you use it, and white when you're all through with it?
I am what remains when nothing is left.What am I?
Tool of thief, toy of queen. Always used to be unseen. Sign of joy, sign of sorrow. Giving all likeness borrowed.
I will disappear every time you say my name.