The northern lights
how do they get there colors you ask?
Aurora Borealis get there colors by the suns radiates all visible colors, which is why sunlight appears white but we see different colors do to the amount of green house gasses changing the color.
how do we know when they are coming?
We know they are coming when the sun shots off solar flares but they don't reach the earth so the expect them to come at any time after they discover the flares. The sentience work hard to find this out for us.