Answer:
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.
I grow where no flower grows, where no light touches the walls, up or down, that I don't care, was here before people were.
My life can be measured in hours, I serve by being devoured. Thin, I am quick. Fat, I am slow. Wind is my foe.
Golden treasure I contain, Guarded by hundreds and thousands. Stored in a labyrinth where no man walks, Yet men come often to seize my gold. By smoke I am overcome and robbed, then left to build my treasure anew
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.
What do you purposefully put lots of in and on your body, but run away from when you encounter it outside?