Answer:
Sleeping during the day, I hide away. Watchful through the night, I open at dawn's light. But only for the briefest time, do I shine. And then I hide away. And sleep through the day.
When liquid splashes me, none seeps through. When I am moved a lot, liquid I spew. When I am hit, color I change. And color, I come in quite a range. What I cover is very complex, and I am very easy to flex.
What is often returned, but never borrowed/
At the sound of me, one may dream or stamp their feet, At the sound of me, one may laugh or sometimes weep.
Iron roof, glass walls, burns and burns and never falls.
They are many and one, they wave and they drum, Used to cover a state, they go with you everywhere.