What does it mean when sky is white?
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Blue light is scattered in all directions by the tiny molecules of air in Earth's atmosphere. Blue is scattered more than other colors because it travels as shorter, smaller waves. This is why we see a blue sky most of the time. Closer to the horizon, the sky fades to a lighter blue or white.
Air molecules that make up the sky are much smaller. "They tend to only be able to scatter out the color blue, making the sky look blue." Clouds are white because all the colors of the rainbow spread out inside them, creating a white appearance.
As far as wavelengths go, Earth's sky really is a bluish violet. But because of our eyes we see it as pale blue.
Scientists have long suspected that one oft-discussed geoengineering technique -- shooting tiny sulfate particles into the upper atmosphere to deflect sunlight -- could turn the blue sky white. Nature has already provided a basic proof of concept.
The reason we see the sky as blue is because the molecules in the air scatter the light absorbing most wavelengths of light except for blue. In addition to this the sky is gray and overcast because of the water droplets in the atmosphere in the forms of clouds and humidity.
When light hits the air molecules in our atmosphere, its colors are scattered in all directions. Blue light is scattered more because of its short, choppy wavelength, making it the color we see the most.
Due to this blue color predominates and the sky appears blue.
Because human eyes are more receptive to the blue wavelengths than the violet ones, it is the scattered blue wavelengths that we see, and why the daytime sky appears blue (and not pink) when we look up at it. The primary radiation scattering process in the atmosphere is called Rayleigh scattering.
Clouds are white because light from the Sun is white. As light passes through a cloud, it interacts with the water droplets, which are much bigger than the atmospheric particles that exist in the sky.
Why the sky is so beautiful?
Think of the Earth's atmosphere as a prism separating the sunlight into its seven colours. However, they all are not scattered the same. The shorter the wavelength, the faster the scattering upon entering the atmosphere. The more scattered a wavelength is, the better we see the colour.
Nitrogen and oxygen make up most of the molecules in our atmosphere, but any gas or aerosol suspended in the air will scatter rays of sunlight into separate wavelengths of light. Consequently, when there are more aerosols in the atmosphere, more sunlight is scattered, resulting in more colorful skies.

If we add up all the light coming from galaxies (and the stars within them), and from all the clouds of gas and dust in the Universe, we'd end up with a colour very close to white, but actually a little bit 'beige'.
According to BBC Science Focus Magazine, most mirrors are technically white with a slight green tinge. According to Live Science, color is a result of reflected light. To produce color, objects absorb some wavelengths of light while reflecting others.
Well when the sun sets, it is lower down and the light has further to travel. Light is made up of all different colours - that's why we get rainbows. Blue light can't travel very far so much of it 'scatters' out before it reaches us. But red light can, which is why the sky appears more red and pink than usual.
So, what about the clouds? In a cloud, sunlight (which is white) is scattered by millions of relatively large water droplets. These droplets scatter all colors almost equally, meaning that the sunlight continues to remain white. This is why clouds appear white against the background of a blue sky.
Without an atmosphere the sky appears black, as evidenced by the lunar sky in pictures taken from the moon. But even a black sky has some lightness. At night, the sky always has a faint color, called "skyglow" by astronomers.
The color of the sun is white. The sun emits all colors of the rainbow more or less evenly and in physics, we call this combination "white". That is why we can see so many different colors in the natural world under the illumination of sunlight.
Grey and gray are two different spellings of the same word. Gray is more common in the U.S., while grey is more common in other English-speaking countries. In proper names—like Earl Grey tea and the unit Gray, among others—the spelling stays the same, and they need to be memorized.
The main phenomenon behind the colour of the sky is due to scattering. When sunlight passes through the atmosphere, the fine particles in the air scatter the blue colour (shorter wavelengths) more strongly than red. The scattered blue light enters our eyes.
What if the sky was red?
Red skies suggest that the clouds are filled with a lot of dust and moisture. If there is a red sky at sunset, it is due to high levels of pressure and stable air conditions that are coming in from the west.
A red sky appears when dust and small particles are trapped in the atmosphere by high pressure. This scatters blue light leaving only red light to give the sky its notable appearance. A red sky at sunset means high pressure is moving in from the west, so therefore the next day will usually be dry and pleasant.
It is occasionally green, though not often. Let's begin...at the beginning. Color in the sky comes from particles; what meteorologists call aerosols that scatter the light. These can come from many sources-pollen, dust, smoke particles, pollutants.
The ocean is blue because water absorbs colors in the red part of the light spectrum. Like a filter, this leaves behind colors in the blue part of the light spectrum for us to see. The ocean may also take on green, red, or other hues as light bounces off of floating sediments and particles in the water.
Sunlight, or visible light, is made of all the rainbow colors: red, orange, yellow, green, blue, indigo, and violet.