Often, they made up rhymes to help them remember useful weather signs. Red skies at sunset delighted many sailors on long ocean voyages. That's because of the way the atmosphere scatters sunlight into the colors of the rainbow.
Blue light is scattered the most.
That's why the sky appears to be brilliantly blue on a sunny day. On a rainy or humid day, particles of dust in the air absorb the moisture and swell to a size that scatters all the colors of light equally. So even on a clear day, the sky may turn grayish white. At sunset, when the sun is low in the sky, its light must travel a longer distance through the atmosphere than it does during midday. The white sunlight is split into reds, yellows, and blues.