Answer:
Without a bridle or a saddle across a thing I ride a-straddle. And those I ride by help of me though almost blind are made to see.
I mirror your actions.
I go into the water black and come out red. What am I?
Many people own a copy of me. Without me the world would fall.
What has feet and legs, and nothing else?
Whoever made me don't want me. Whoever bought me don't need me. Whoever use me don't know me.