Answer:
What has 3 feet but cannot walk?
Sometimes black, sometimes white, I have veins but no blood
When you stop and look, you can always see me. If you try to touch, you cannot feel me. I cannot move, but as you near me, I will move away from you.
Long and think, red within, with a nail at the end.
I sleep by day, I fly by night. I have no feathers to aid my flight.
Almost everyone needs it, asks for it, gives it. But almost nobody takes it.