Sky blue is a colour that resembles that of an unclouded sky around noon reflecting off a metallic surface. The entry for "sky-blue" in Murray's New English Dictionary reports a first sighting of the term in the article on "silver" in Ephraim Chambers's Cyclopaedia of 1728.

Why was the sky was blue?

The Short Answer:

Gases and particles in Earth's atmosphere scatter sunlight in all directions. Blue light 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.

What is the sky is blue?

As white light passes through our atmosphere, tiny air molecules cause it to 'scatter'. The scattering caused by these tiny air molecules (known as Rayleigh scattering) increases as the wavelength of light decreases. ... Therefore, blue light is scattered more than red light and the sky appears blue during the day.