What time is it when you see cows sleeping in a field?

I come in the morning, I come in the night. I am not quite dark, I am not quite light. I bring the sun, or take it away, I am the transition of the day. What am I?

I appear as yellow but I'm actually white, Nuclear fusion gives me my bite. Often featured on a coloring page corner, The Universe is my stage and I'm the center of the order. What am I?

I eat gas, make it more heavy. When I die, I'm an old Chevy.

Am I white on black Or black on white? The world may never know