Answer:
When it comes to me you go on red and stop on green.
I'm really blue but when you see me I'm red. You don't see me too often. I'm there for you if you're hurt.
I am rubber you can eat!
I am shared by goats devils and unicorns.
You throw me out when you use me and take me in when you are done.
As round as an apple. As deep as a cup. All the king's horses can't pull it up.