So, if Superman gets his powers from the color of our sun, why doesn't he lose said powers at night? What's up with that?

He's like a battery, he stores it up. If he were out of the sun for a prolonged period (see "Dark Knight Returns") he'd be in trouble.

I always thought he got his power from the sun, and that power didn't come from the color, but from a property found only in yellow suns.

But...why does the justice league always go to other planetary systems?

Still some sunlight coming his way at night, reflected off of the moon.

Why don't plants die at night? Why don't you die when you are not eating?

Supe stores it. that simple.