Belt is the answer
I can be red or green or yellow. I'll help you stay a healthy fellow. Inside, I am white; I do not emit light. But if you look just right, I hold a star. What am I?
People walk in and out of me. They push and I follow. When they walk out on me, I close up and I stay waiting for the next person to walk into my life when I have a more open mind. What am I ??