Answer:
Thirty white horses on a red hill, first they champ, then they stamp, then they stand still.
My first is nothing but a name; my second is more small; my whole is of so little fame it has no name at all.
When I live I cry, If you don't kill me I'll die.
In the evening I'm long, in the morning I'm small; When seen in a ballroom, I'm nothing at all.
I can travel from there to here by disappearing, and here to there by reappearing.
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.